GLASS-CERAMIC HAVING SPECIFIC THERMAL EXPANSION CHARACTERISTICS
20240092687 ยท 2024-03-21
Assignee
Inventors
Cpc classification
C03C3/087
CHEMISTRY; METALLURGY
C03C2214/16
CHEMISTRY; METALLURGY
C03C10/0027
CHEMISTRY; METALLURGY
International classification
Abstract
A lithium aluminum silicate (LAS) glass-ceramic has an average coefficient of thermal expansion (CTE) in a range from 0 to 50? C. of at most 0?0.1?10.sup.?6/K and a thermal hysteresis at least in a temperature range from 15? C. to 35? C. of <0.1 ppm. The LAS glass-ceramic includes (in mol % based on oxide): SiO.sub.2 60-<70; Li.sub.2O 7-9.6; MgO+ZnO>0.5-1.5; R.sub.2O>0.5, where R.sub.2O is Na.sub.2O and/or K.sub.2O and/or Cs.sub.2O and/or Rb.sub.2O; and nucleating agent with a content of 1.5 to 6 mol %. The nucleating agent is at least one component selected from the group consisting of TiO.sub.2, ZrO.sub.2, Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, SnO.sub.2, MoO.sub.3, WO.sub.3 and HfO.sub.2.
Claims
1. A lithium aluminum silicate (LAS) glass-ceramic having an average coefficient of thermal expansion (CTE) in a range from 0 to 50? C. of at most 0?0.1?10.sup.?6/K and a thermal hysteresis at least in a temperature range from 15? C. to 35? C. of <0.1 ppm and comprising components as follows (in mol % based on oxide): TABLE-US-00009 SiO.sub.2 60-<70; Li.sub.2O 7-9.6; MgO + ZnO >0.5-1.5;.sup. R.sub.2O >0.5, where R.sub.2O is Na.sub.2O and/or K.sub.2O and/or Cs.sub.2O and/or Rb.sub.2O; and nucleating agent with a content of 1.5 to 6 mol %, wherein the nucleating agent is at least one component selected from the group consisting of TiO.sub.2, ZrO.sub.2, Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, SnO.sub.2, MoO.sub.3, WO.sub.3 and HfO.sub.2.
2. The LAS glass-ceramic of claim 1, comprising Al.sub.2O.sub.3 with a content of 10 to 22 mol %.
3. The LAS glass-ceramic of claim 1, wherein the content of the sum total of ZnO+MgO is ?0.55 mol % and/or <1.5 mol %.
4. The LAS glass-ceramic of claim 1, wherein the content of SiO.sub.2 is ?69.5 mol %.
5. The LAS glass-ceramic of claim 1, wherein a content of a sum total of RO (CaO+BaO+SrO) is ?0.1 mol % and/or is ?6 mol %.
6. The LAS glass-ceramic of claim 1, wherein the content of the sum total of R.sub.2O (Na.sub.2O+K.sub.2O+Cs.sub.2O+Rb.sub.2O) is ?0.55 mol % and/or is ?6 mol %.
7. The LAS glass-ceramic of claim 1, wherein the nucleating agent comprises a plurality of components and a content of a sum total of the components is ?2.5 mol % and/or is ?5 mol %.
8. The LAS glass-ceramic of claim 1, wherein the following condition is applicable: molar content of SiO.sub.2+(5?molar content of Li.sub.2O)?105; and/or wherein the following condition is applicable: molar content of SiO.sub.2+(5?molar content of Li.sub.2O)?115.5.
9. The LAS glass-ceramic of claim 1, wherein a processing temperature Va is not more than 1330? C.
10. The LAS glass-ceramic of claim 1, wherein a main crystal phase is high quartz solid solution.
11. The LAS glass-ceramic of claim 10, wherein an average crystallite size of the high quartz solid solution is <100 nm and/or a crystal phase fraction is less than 75 vol %.
12. The LAS glass-ceramic of claim 1, wherein an index F is <1.20, where F=TCL (0; 50? C.)|expansion (0; 50? C.)|, where TCL is a total change of length.
13. The LAS glass-ceramic of claim 1, wherein an alternative index f.sub.(20;40) is <0.024 ppm/K and/or an alternative index f.sub.(20;70) is <0.039 ppm/K and/or an alternative index f.sub.(?10;30) is <0.015 ppm/K.
14. The LAS glass-ceramic of claim 1, having a relative change in length (dl/l.sub.0) of ?|0.10| ppm in a temperature range from 20? C. to 30? C. and/or a relative change in length (dl/l.sub.0) of ?|0.17| ppm in a temperature range from 20? C. to 35? C.
15. The LAS glass-ceramic of claim 1, having a relative change in length (dl/l.sub.0) of ?|0.30| ppm in a temperature range from 20? C. to 40? C.
16. The LAS glass-ceramic of claim 1, wherein a CTE-T curve in a temperature interval having a breadth of at least 30 K has a slope of ?0?2.5 ppb/K.sup.2.
17. The LAS glass-ceramic of claim 1, having a thermal hysteresis of <0.1 ppm at least in a temperature range from 15? C. to 40? C.
18. A precision component, comprising: a lithium aluminum silicate (LAS) glass-ceramic having an average coefficient of thermal expansion CTE in a range from 0 to 50? C. of at most 0?0.1?10.sup.?6/K and a thermal hysteresis at least in a temperature range from 15? C. to 35? C. of <0.1 ppm and comprising components as follows (in mol % based on oxide): TABLE-US-00010 SiO.sub.2 60-<70; Li.sub.2O 7-9.6; MgO + ZnO >0.5-1.5;.sup. R.sub.2O >0.5, where R.sub.2O is Na.sub.2O and/or K.sub.2O and/or Cs.sub.2O and/or Rb.sub.2O; and nucleating agent with a content of 1.5 to 6 mol %, where the nucleating agent is at least one component selected from the group consisting of TiO.sub.2, ZrO.sub.2, Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, SnO.sub.2, MoO.sub.3, WO.sub.3 and HfO.sub.2.
19. The precision component of claim 18, wherein the LAS glass-ceramic comprises Al.sub.2O.sub.3 with a content of 10 to 22 mol %.
20. The precision component of claim 18, wherein the content of the sum total of ZnO+MgO is ?0.55 mol % and/or <1.5 mol %.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawing(s), wherein:
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[0038] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
DETAILED DESCRIPTION OF THE INVENTION
[0039] A subject provided according to the invention is a lithium aluminum silicate (LAS) glass-ceramic having an average coefficient of thermal expansion CTE in the range from 0 to 50? C. of at most 0?0.1?10.sup.?6/K and a thermal hysteresis at least in the temperature range of 15? C.-35? C. of <0.1 ppm and comprising the following components (in mol % based on oxide):
TABLE-US-00001 SiO.sub.2 .sup.60-<70 Li.sub.2O .sup.7-9.6 MgO + ZnO >0.5-1.5 R2O >0.5
where R.sub.2O may be Na.sub.2O and/or K.sub.2O and/or Cs.sub.2O and/or Rb.sub.2O, and nucleating agent with a content of 1.5 to 6 mol %, where nucleating agent is at least one component selected from the group consisting of TiO.sub.2, ZrO.sub.2, Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, SnO.sub.2, MoO.sub.3, WO.sub.3, HfO.sub.2.
[0040] The invention provides an LAS glass-ceramic (also called glass-ceramic below) that combines a number of relevant properties: it can be produced with high homogeneity in industrial-scale production plants. Additionally, it has an average coefficient of thermal expansion CTE in the range from 0 to 50? C. of at most 0?0.1?10.sup.?6/K, i.e. it has zero expansion. Moreover, it has a thermal hysteresis of <0.1 ppm at least in the temperature range from 15? C. to 35? C. A material having such a low hysteresis effect of <0.1 ppm within the stated temperature range is referred to hereinafter as hysteresis-free. Since the extent of the hysteresis, as already mentioned above, is dependent on the rate of temperature change used to ascertain it, the statements relating to hysteresis in the context of the invention refer to a heating rate/cooling rate of 36 K/h, i.e. 0.6 K/min. The low thermal hysteresis in the stated temperature range reduces the cost and effort for compensating thermally induced deformations of a precision component over time when the material is used in a precision component, especially in an EUV lithography component. In some embodiments, the LAS glass-ceramic may at least in the temperature range of 15? C. to 40? C., optionally at least in the temperature range of 15? C. to 45? C., optionally at least in the temperature range from 15? C. to 50? C. or at least in the temperature range from 10? C. to 35? C., be hysteresis-free.
[0041] The features of CTE and thermal hysteresis are described in detail further herein.
[0042] A glass-ceramic provided in accordance with the invention comprehends non-porous inorganic materials having a crystalline phase and a vitreous phase, with the matrix, i.e. the continuous phase, generally being a glass phase. For production of the glass-ceramic, first of all, the components of the glass-ceramic are mixed, melted and refined, and what is called a green glass is cast. The green glass, after cooling, is crystallized in a controlled manner by reheating (so-called controlled volume crystallization). The chemical composition (analysis) of the green glass and of the glass-ceramic produced from it are the same; ceramization alters solely the internal structure of the material. Therefore, where reference is made hereinafter to the composition of the glass-ceramic, the statements made are equally applicable to the precursor article of the glass-ceramic, i.e. to the green glass.
[0043] In the prior art, it was assumed to date that the glass components MgO and ZnO in combination or each individually are necessary, specifically for zero-expansion LAS glass-ceramics, in order to achieve the zero expansion and to make the shape of the CTE-T curve of the material flat, i.e. with a shallow slope of the CTE-T curve within the relevant temperature range. In DE 10 2022 105 929.4, unpublished at the priority date of the present application, it was recognized by the inventors for the first time that the two components MgO and ZnO promote the occurrence of thermal hysteresis within the temperature range under consideration and that therefore it is essential to the provision of a zero-expansion LAS glass-ceramic which is hysteresis-free at least in the temperature range of 10? C. to 35? C. to limit the MgO and ZnO content or even to omit them entirely. Consequently, there was a conflict of objectives in that an LAS glass-ceramic could be either zero-expansion or hysteresis-free.
[0044] This conflict of objectives was resolved, with the technical teaching of DE 10 2022 105 929.4, unpublished at the priority date of the present application, by not only doing largely without the use of MgO and ZnO but also selecting the SiO.sub.2 and Li.sub.2O contents from stipulated ranges as well.
[0045] A problem affecting these zero-expansion and hysteresis-free glass-ceramics, however, can be the establishment of the profile for the expansion curve and hence for the CTE. The expansion curves for the glass-ceramics with a low sum total of MgO+ZnO in some cases, rather than being flat as desired, are sharply curved specifically within the temperature range between 0? C. and 50? C. The inventors have discovered that through a deliberate addition of more than 0.5 mol % of alkali metal oxides (R.sub.2O), selected from the group consisting of Na.sub.2O and/or K.sub.2O and/or Cs.sub.2O and/or Rb.sub.2O, glass-ceramics with a flat expansion curve are obtained, surprisingly, and hence also the total MgO+ZnO content, as claimed in the context of the present invention, can be higher with addition of more than 0.5 mol % of R.sub.2O, with the resulting glass-ceramics nevertheless being hysteresis-free at least in the temperature range from 15? C. to 35? C.that is, in a temperature interval which includes room temperature.
[0046] LAS glass-ceramics contain a negatively expanding crystal phase which, in accordance with the invention, may advantageously comprise or consist of high quartz solid solution, also called ?-eucryptite, and a positively expanding glass phase. As well as SiO.sub.2 and Al.sub.2O.sub.3, Li.sub.2O is a main constituent of the solid solution. If present, ZnO and/or MgO are likewise incorporated into the solid solution phase, and together with Li.sub.2O influence the expansion characteristics of the crystal phase. In contrast to the known zero-expansion glass-ceramics in which MgO and ZnO in particular are used for establishing the desired expansion characteristics of the glass-ceramic, the invention for this purpose uses R.sub.2O, where R.sub.2O may be Na.sub.2O and/or K.sub.2O and/or Rb.sub.2O and/or Cs.sub.2O. Unlike MgO and ZnO, however, the stated alkali metal oxides remain in the glass phase and are not incorporated into the high quartz solid solution.
[0047] In the context of the invention, it has been found that for the provision of a zero-expansion and hysteresis-free glass-ceramic, it may be advantageous if the composition meets the condition of molar content of SiO.sub.2+(5?molar content of Li.sub.2O)?105, optionally ?105.5, optionally ?106 or optionally ?106.5, optionally molar content of SiO.sub.2+(5?molar content of Li.sub.2O)?107 or ?107.5. Alternatively or additionally, for the condition of molar content SiO.sub.2+(5?molar content of Li.sub.2O), an advantageous upper limit of ?115.5 or of ?114.5 or of ?113.5 may apply.
[0048] In some embodiments, the glass-ceramic may comprise the following components, individually or in any combination, in mol %:
TABLE-US-00002 Al.sub.2O.sub.3 10 to 22 P.sub.2O.sub.5 0 to 6 MgO .sup.0 to 1.1 ZnO .sup.0 to 1.5 R.sub.2O >0.5 to 6.sup. RO 0 to 6 TiO.sub.2 + ZrO.sub.2 1.5 to 6.
[0049] In some embodiments, within the scope of the limits stated above for the sum totals of R.sub.2O, RO and TiO.sub.2+ZrO.sub.2, the glass-ceramic may contain the following components, individually or in any combination, in mol %:
TABLE-US-00003 Na.sub.2O 0 to 3 K.sub.2O 0 to 3 Cs.sub.2O 0 to 2 Rb.sub.2O 0 to 2 CaO 0 to 5 BaO 0 to 4 SrO 0 to 3 TiO.sub.2 0 to 5 ZrO.sub.2 0 to 3.
[0050] In some embodiments, the LAS glass-ceramic comprises (in mol % based on oxide):
TABLE-US-00004 Al.sub.2O.sub.3 10 to 22 P.sub.2O.sub.5 0 to 6 MgO .sup.0 to 1.0 ZnO .sup.0 to 1.4 R2O 0.6 to 5.sup. RO 0 to 6 Nucleating agent 1.5 to 6,
where nucleating agent is optionally TiO.sub.2 and/or ZrO.sub.2.
[0051] In some embodiments, the LAS glass-ceramic comprises (in mol % based on oxide):
TABLE-US-00005 SiO.sub.2 60.50 to 69 Li.sub.2O .sup.8 to 9.6 Al.sub.2O.sub.3 11 to 21 P.sub.2O.sub.5 0 to 4 MgO .sup.0 to 1.1 ZnO .sup.0 to 1.5 R2O >0.5 to 4.sup. RO 0.2 to 4.5 Nucleating agent 2.5 to 5,
where nucleating agent is optionally TiO.sub.2 and/or ZrO.sub.2.
[0052] The glass-ceramic contains a fraction of silicon dioxide (SiO.sub.2) of at least 60 mol %, optionally at least 60.5 mol %, optionally at least 61 mol %, optionally at least 61.5 mol %, optionally at least 62.0 mol %. The fraction of SiO.sub.2 is less than 70 mol %, optionally at most 69.5 mol %, optionally at most 69 mol %, optionally at most 68.5 mol %. With larger fractions of SiO.sub.2, the batch is more difficult to melt, and the viscosity of the melt is higher, which can lead to problems affecting the homogenization of the melts in industrial-scale production plants. The SiO.sub.2 content ought therefore to be less than 70 mol %. If the viscosity of a melt is high, there is an increase in the processing temperature Va of the melt. Refining and homogenization of the melt require very high temperatures, which, however, mean that the increasing aggressiveness of the melt with temperature results in attacks on the linings of the melting assemblies. Moreover, even higher temperatures may not be enough to generate a homogeneous melt, with the consequence that the green glass may have stria and inclusions (especially bubbles and particles originating from the lining of the melting assemblies), so that, after ceramization, the glass-ceramic that is produced fails to meet the requirements in terms of homogeneity of properties, such as the homogeneity of the coefficient of thermal expansion, for example. SiO.sub.2 contents lower than the stated upper limit may be used for this reason.
[0053] The fraction of Al.sub.2O.sub.3 may be at least 10 mol %, optionally at least 11 mol %, optionally at least 12 mol %, optionally at least 13 mol %, optionally at least 14 mol %, optionally at least 14.5 mol %, optionally at least 15 mol %. If the content is too low, formation of low-expansion solid solution is inadequate or absent. The fraction of Al.sub.2O.sub.3 may be at most 22 mol %, optionally at most 21 mol %, optionally at most 20 mol %, optionally at most 19.0 mol %, optionally at most 18.5 mol %. Too high an Al.sub.2O.sub.3 content leads to increased viscosity and promotes uncontrolled devitrification of the material.
[0054] The glass-ceramic provided according to the invention may contain 0 to 6 mol % of P.sub.2O.sub.5. The P.sub.2O.sub.5 phosphate content of the glass-ceramic may be at least 0.1 mol %, optionally at least 0.3 mol %, optionally at least 0.5 mol %, optionally at least 0.6 mol %, optionally at least 0.7 mol %, optionally at least 0.8 mol %. P.sub.2O.sub.5 is incorporated substantially into the crystal phase of the glass-ceramic and has positive influence on the expansion characteristics of the crystal phase and hence of the glass-ceramic. Moreover, melting of the components and refining characteristics of the melt are improved. If, however, too much P.sub.2O.sub.5 is present, the profile of the CTE-T curve in the 0? C. to 50? C. temperature range does not exhibit an advantageous flat progression. Advantageously, therefore, there ought to be not more than 6 mol %, optionally not more than 5 mol %, optionally at most 4 mol %, optionally less than 4 mol % of P.sub.2O.sub.5 present in the glass-ceramic. In some embodiments, the glass-ceramics may be free of P.sub.2O.sub.5.
[0055] In the context of the invention, certain sum totals and proportions of the components SiO.sub.2, Al.sub.2O.sub.3 and/or P.sub.2O.sub.5, i.e. of the components which form the high quartz solid solution, may be conducive to the formation of a glass-ceramic provided according to the invention.
[0056] The cumulative fraction in mol % of the SiO.sub.2 and Al.sub.2O.sub.3 base constituents of the LAS glass-ceramic may be at least 75 mol %, optionally at least 78 mol %, optionally at least 79 mol %, optionally at least 80 mol % and/or optionally at most 90 mol %, optionally at most 87 mol %, optionally at most 86 mol %, optionally at most 85 mol %. If this sum total is too high, the viscosity curve of the melt is shifted to higher temperatures, which is disadvantageous, as already elucidated above in connection with the SiO.sub.2 component. If the sum total is too low, too little solid solution is formed.
[0057] The cumulative fraction in mol % of the SiO.sub.2, Al.sub.2O.sub.3 and P.sub.2O.sub.5 base constituents of the LAS glass-ceramic is optionally at least 77 mol %, optionally at least 81 mol %, optionally at least 83 mol %, optionally at least 84 mol % and/or optionally at most 91 mol %, optionally at most 89 mol %, optionally at most 87 mol %, optionally at most 86 mol %.
[0058] The ratio of the mol % fractions of P.sub.2O.sub.5 to SiO.sub.2 is optionally at least 0.005, optionally at least 0.01, optionally at least 0.012 and/or optionally at most 0.1, optionally at most 0.08, optionally at most 0.07.
[0059] As a further constituent, the glass-ceramic contains lithium oxide (Li.sub.2O) in a fraction of at least 7 mol %, optionally at least 7.5 mol %, optionally at least 8 mol %, optionally at least 8.25 mol %. The fraction of Li.sub.2O is limited to at most 9.6 mol %, optionally at most 9.5 mol %, optionally at most 9.4 mol %, optionally at most 9.35 mol %, optionally at most or less than 9.3 mol %. Li.sub.2O is a constituent of the solid solution phase and makes a substantial contribution to the thermal expansion of the glass-ceramic. The stated upper limit of 9.6 mol % ought not to be exceeded, since otherwise, in spite of the total MgO+ZnO content according to the invention, the resulting glass-ceramics have a negative coefficient of thermal expansion CTE (0;50). If the Li.sub.2O content is less than 7 mol %, too little solid solution is formed and the CTE of the glass-ceramic remains positive.
[0060] The glass-ceramic provided according to the invention contains more than 0.5 mol % of alkali metal oxide R.sub.2O, where R.sub.2O may be Na.sub.2O and/or K.sub.2O and/or Cs.sub.2O and/or Rb.sub.2O. In accordance with the invention, surprisingly, an R.sub.2O content of more than 0.5 mol % contributes to producing a glass-ceramic having a flat profile of the expansion curve, even with a relatively high sum total of MgO+ZnO. The sum total R.sub.2O for the Na.sub.2O, K.sub.2O, Cs.sub.2O and Rb.sub.2O contents may be at least 0.55 mol %, optionally at least 0.6 mol %, optionally at least 0.65 mol %, optionally at least 0.7 mol %, optionally at least 0.75 mol %. Certain variants may contain at least 0.8 mol %, optionally at least 0.85 mol %, optionally at least 0.9 mol %, optionally at least 0.95 mol %, optionally at least 1.0 mol % of R.sub.2O. The sum total R.sub.2O for the Na.sub.2O, K.sub.2O, Cs.sub.2O and Rb.sub.2O contents may be at most 6 mol %, optionally at most 5 mol %, optionally at most 4 mol %, optionally at most 3 mol %, optionally at most 2.5 mol %. If the sum total of Na.sub.2O+K.sub.2O+Cs.sub.2O+Rb.sub.2O is too low or too high, it can be possible that the CTE (0;50) targeted by the invention is not achieved. Too much R.sub.2O in the glass-ceramic, however, impairs the chemical resistance of the material. If the sum total of Na.sub.2O+K.sub.2O+Cs.sub.2O+Rb.sub.2O is too low, the expansion curve for the material exhibits a curved portion in the temperature range under consideration, and the glass-ceramic with a total MgO+ZnO content in accordance with the invention is not hysteresis-free in the sense of the invention.
[0061] Within the limits stated above for the sum total of R.sub.2O, the individual components sodium oxide (Na.sub.2O), potassium oxide (K.sub.2O), caesium oxide (Cs.sub.2O) and rubidium oxide (Rb.sub.2O) are present optionally in the glass-ceramic, meaning that Na.sub.2O-free and/or K.sub.2O-free and/or Cs.sub.2O-free and/or Rb.sub.2O-free variants are possible. The fraction of Na.sub.2O may be at most 3 mol %, optionally at most 2 mol %, optionally at most 1.7 mol %, optionally at most 1.5 mol %, optionally at most 1.3 mol %, optionally at most 1.1 mol %. The fraction of K.sub.2O may be at most 3 mol %, optionally at most 2.5 mol %, optionally at most 2 mol %, optionally at most 1.8 mol %, optionally at most 1.7 mol %. The fraction of Cs.sub.2O may be at most 2 mol %, optionally at most 1.5 mol %, optionally at most 1 mol %, optionally at most 0.6 mol %. The fraction of Rb.sub.2O may be at most 2 mol %, optionally at most 1.5 mol %, optionally at most 1 mol %, optionally at most 0.6 mol %. According to some embodiments, the glass-ceramics are free of Na.sub.2O and/or K.sub.2O and/or Cs.sub.2O and/or Rb.sub.2O.
[0062] Na.sub.2O and K.sub.2O, in each case and independently of one another, may be present in a fraction of at least 0.05 mol %, optionally at least 0.1 mol %, optionally at least 0.15 mol %, optionally at least 0.2 mol %, optionally at least 0.25 mol %, optionally at least 0.3 mol %, optionally at least 0.35 mol %, optionally at least 0.4 mol %, optionally at least 0.45 mol %, optionally at least 0.5 mol %, in the glass-ceramic. The stated limits may also apply for Cs.sub.2O and Rb.sub.2O. The Na.sub.2O, K.sub.2O, Cs.sub.2O and Rb.sub.2O components remain substantially in the amorphous glass phase of the glass-ceramic and may be important for preserving the zero expansion of the ceramized material.
[0063] The glass-ceramic may contain at least one alkaline earth metal oxide selected from the group consisting of CaO, BaO and SrO, with this group being referred to collectively as RO. The components from the RO group remain essentially in the amorphous glass phase of the glass-ceramic and may be important for preserving the zero expansion of the ceramized material. If the sum total of CaO+BaO+SrO is too high, the target CTE (0;50) provided according to the invention is not achieved. Therefore, the fraction of RO is optionally at most 6 mol % or at most 5.5 mol %, optionally at most 5 mol %, optionally at most 4.5 mol %, optionally at most 4 mol %, optionally at most 3.8 mol %, optionally at most 3.5 mol %, optionally at most 3.2 mol %. If the glass-ceramic contains RO, an advantageous lower limit may be at least 0.1 mol %, optionally at least 0.2 mol %, optionally at least 0.3 mol %, optionally at least 0.4 mol %. According to some embodiments, the glass-ceramics may be free of RO.
[0064] The fraction of CaO may optionally be at most 5 mol %, optionally at most 4 mol %, optionally at most 3.5 mol %, optionally at most 3 mol %, optionally at most 2.8 mol %, optionally at most 2.6 mol %. The glass-ceramic may optionally contain at least 0.1 mol %, optionally at least 0.2 mol %, optionally at least 0.4 mol %, optionally at least 0.5 mol % of CaO. The glass-ceramic may optionally contain the component BaO, which is a good glass-former, in a fraction of at least 0.1 mol %, optionally at least 0.2 mol % and/or at most 4 mol %, optionally at most 3 mol %, optionally at most 2.5 mol %, optionally at most 2 mol %, optionally at most 1.5 mol %, optionally at most 1.4 mol %. The glass-ceramic may contain SrO in a fraction of at most 3 mol %, optionally at most 2 mol %, optionally at most 1.5 mol %, optionally at most 1.3 mol %, optionally at most 1.1 mol %, optionally at most 1 mol %, optionally at most 0.9 mol % and/or optionally at least 0.1 mol %. According to some embodiments, the glass-ceramics are free from CaO and/or BaO and/or SrO. According to some embodiments, the glass-ceramic contains CaO.
[0065] The glass-ceramic provided according to the invention has a sum total of MgO+ZnO in the range of >0.5 to 1.5 mol %. An advantageous lower limit for the sum total may be at least 0.55 mol %, optionally at least 0.6 mol %, optionally at least 0.65 mol %, optionally at least 0.7 mol %, optionally at least 0.75 mol %. At maximum, the glass-ceramic contains 1.5 mol % of MgO+ZnO. An advantageous upper limit may be less than 1.5 mol %, optionally not more than 1.45 mol %, optionally not more than 1.4 mol %, optionally not more than 1.35 mol %, optionally not more than 1.3 mol %, optionally not more than 1.25 mol %, optionally not more than 1.2 mol %, optionally not more than 1.15 mol %, optionally not more than 1.1 mol %, optionally not more than 1.05 mol %, optionally not more than 1.0 mol %, optionally not more than 0.95 mol %. If the sum total of MgO+ZnO is too high, the glass-ceramics have a thermal hysteresis of >0.1 ppm in the temperature range of 15? C. to 35? C.
[0066] The glass-ceramic may contain magnesium oxide (MgO) with a content of 0 to 1.1 mol %. An advantageous MgO upper limit may be 1.1 mol %. If the MgO content is too high, the material exhibits a thermal hysteresis of 0.1 ppm or more in the claimed temperature range. A further advantageous upper limit may be not more than 1.05 mol %, not more than 1.0 mol %, not more than 0.95 mol %, not more than 0.9 mol %, not more than 0.85 mol % or not more than 0.8 mol %. The addition of MgO may be useful for keeping the CTE low, especially in the case of relatively high Li.sub.2O contents, for providing a zero-expansion glass-ceramic. If MgO is present in the glass-ceramic, an advantageous MgO lower limit may be 0.05 mol % or 0.1 mol % or 0.15 mol % or 0.2 mol % or 0.25 mol % or 0.3 mol %. Certain variants may also contain at least 0.35 mol % or 0.4 mol % or 0.45 mol % or 0.5 mol % or more than 0.5 mol % of MgO. Some embodiments of the glass-ceramic may be free of MgO.
[0067] The glass-ceramic may contain zinc oxide (ZnO) with a content of 0 to 1.5 mol %. An advantageous upper limit may be 1.5 mol %. If the ZnO content is too high, the material exhibits a thermal hysteresis of 0.1 ppm or more in the claimed temperature range. A further advantageous upper limit may be not more than 1.45 mol %, not more than 1.4 mol %, not more than 1.35 mol %, not more than 1.3 mol %, not more than 1.25 mol %, not more than 1.2 mol %, not more than 1.15 mol %, not more than 1.1 mol %, not more than 1.05 or not more than 1.0 mol %. Certain embodiments may also contain not more than 0.95 mol % or not more than 0.9 mol % or not more than 0.85 mol % or not more than 0.8 mol % of ZnO. If ZnO is present in the glass-ceramic, an advantageous ZnO lower limit may be 0.05 mol % or 0.1 mol % or 0.15 mol % or 0.2 mol % or 0.25 mol % or 0.3 mol %. Certain variants may also contain 0.35 mol % or 0.4 mol % or 0.45 mol % or 0.5 mol % or more than 0.5 mol % of ZnO. Some embodiments of the glass-ceramic may be free of ZnO.
[0068] The glass-ceramic further contains at least one crystal nucleating agent selected from the group consisting of TiO.sub.2, ZrO.sub.2 Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, SnO.sub.2, MoO.sub.3, WO.sub.3 and HfO.sub.2. Nucleating agent may be a combination of two or more of the stated components. A further advantageous nucleating agent may be HfO.sub.2. In some embodiments, therefore, the glass-ceramic comprises HfO.sub.2 and at least one crystal nucleating agent selected from the group consisting of TiO.sub.2, ZrO.sub.2 Ta.sub.2O.sub.5, Nb.sub.2O.sub.5, SnO.sub.2, MoO.sub.3 and WO.sub.3. The sum total of the fractions of the nucleating agents is optionally at least 1.5 mol %, optionally at least 2 mol % or more than 2 mol %, optionally at least 2.5 mol %, in certain variants at least 3 mol %. An upper limit may be not more than 6 mol %, optionally not more than 5 mol %, optionally not more than 4.5 mol % or not more than 4 mol %. In some embodiments, the stated upper and lower limits are applicable to the sum total of TiO.sub.2 and ZrO.sub.2.
[0069] The glass-ceramic may contain titanium oxide (TiO.sub.2) optionally with a fraction of at least 0.1 mol %, optionally at least 0.5 mol %, optionally at least 1.0 mol %, optionally at least 1.5 mol %, optionally at least 1.8 mol % and/or optionally at most 5 mol %, optionally at most 4 mol %, optionally at most 3 mol %, optionally at most 2.5 mol %, optionally 2.3 mol %. TiO.sub.2-free variants of the glass-ceramic provided according to the invention are possible.
[0070] The glass-ceramic may further contain zirconium oxide (ZrO.sub.2) in a fraction of at most 3 mol %, optionally at most 2.5 mol %, optionally at most 2 mol %, optionally at most 1.5 mol % or at most 1.2 mol %. ZrO.sub.2 may be present optionally in a fraction of at least 0.1 mol %, optionally at least 0.5 mol %, at least 0.8 mol % or at least 1.0 mol %. ZrO.sub.2 free variants of the glass-ceramic provided according to the invention are possible.
[0071] According to some variants provided according to the invention, individually or in total, there may be 0 to 5 mol % of Ta.sub.2O.sub.5 and/or Nb.sub.2O.sub.5 and/or SnO.sub.2 and/or MoO.sub.3 and/or WO.sub.3 present in the glass-ceramic, serving, for example, as alternative or additional nucleating agents or for modulating the optical properties, e.g. refractive index. HfO.sub.2 may likewise be an alternative or additional nucleating agent. For modulating the optical properties it is possible in some variants forfor exampleGd.sub.2O.sub.3, Y.sub.2O.sub.3, HfO.sub.2, Bi.sub.2O.sub.3 and/or GeO.sub.2 to be present.
[0072] The glass-ceramic may further contain one or more customary refining agents, selected from the group consisting of As.sub.2O.sub.3, Sb.sub.2O.sub.3, SnO.sub.2, SO.sub.4, F.sup.?, Cl.sup.?, Br.sup.?, or a mixture thereof, in a fraction of more than 0.05 mol % or at least 0.1 mol % and/or at most 1 mol %. However, fluorine as refining agent may lower the transparency of the glass-ceramic and/or the chemical resistance, and so this component, if present, is limited optionally to not more than 0.5 mol %, optionally not more than 0.3 mol %, optionally not more than 0.1 mol %. The glass-ceramic is optionally free of fluorine.
[0073] According to some embodiments, the glass-ceramic may contain not more than 0.05 mol % of As.sub.2O.sub.3 as refining agent, and according to some embodiments may be free of As.sub.2O.sub.3. It may be advantageous for the glass-ceramic, instead of or in addition to optionally not more than 0.05 mol % of As.sub.2O.sub.3, to comprise at least one alternative redox refining agent and/or at least one evaporating refining agent and/or at least one decomposing refining agent.
[0074] The alternative redox refining agents, which contain multivalent or polyvalent ions able to occur at least in two oxidation states, present in a temperature-dependent equilibrium to one another, where a gas, usually oxygen, is released at high temperatures, include, for example, Sb.sub.2O.sub.3, SnO.sub.2, MnO.sub.2, CeO.sub.2 and Fe.sub.2O.sub.3.
[0075] The evaporating refining agents, which are volatile at high temperatures by virtue of their vapour pressure, include halogens with refining effect, such as Cl, Br and I, for example.
[0076] The decomposing refining agents, which decompose at high temperatures while giving off refining gas, and the decomposition product having a sufficiently high gas pressure, include, for example, salts which contain oxo anions, more particularly a sulfate component, which in materials analysis is determined as SO.sub.3.
[0077] Combinations of the above-stated chemical refining agents may also be advantageous.
[0078] Some embodiments may comprise: [0079] SnO.sub.2 and/or Sb.sub.2O.sub.3 each with maximum 0.05 mol % of As.sub.2O.sub.3; or [0080] As.sub.2O.sub.3-free combinations such as: Sb.sub.2O.sub.3 with SnO2; Sb.sub.2O.sub.3 with Cl, Sb.sub.2O.sub.3 with SO.sub.3; or [0081] As.sub.2O.sub.3-free and Sb.sub.2O.sub.3-free combinations such as: SnO.sub.2 with Cl, SnO.sub.2 with SO.sub.3, Cl with SO.sub.3.
[0082] The above glass compositions may optionally contain additions of coloring oxides, such as, for example, Nd.sub.2O.sub.3, Fe.sub.2O.sub.3, CoO, NiO, V.sub.2O.sub.5, MnO.sub.2, CuO, CeO.sub.2, Cr.sub.2O.sub.3, rare earth oxides in contents of, in each case individually or in total, 0-3 mol %. Some variants are free of colouring oxides.
[0083] B.sub.2O.sub.3 may have an adverse effect on the transparency of the glass-ceramic. The content of this component, therefore, in some variants is limited to <0.2 mol %, optionally at most 0.1 mol %. Some variants are free of B.sub.2O.sub.3.
[0084] According to some embodiments provided according to the present invention, the composition is free of components not mentioned above.
[0085] According to some embodiments provided according to the present invention, the glass-ceramic provided according to the invention or the green glass consists optionally to an extent of at least 90 mol %, optionally to an extent of at least 95 mol %, optionally to an extent of at least 99 mol %, of the abovementioned components, and optionally of the components SiO.sub.2, Al.sub.2O.sub.3, Li.sub.2O, MgO, ZnO, P.sub.2O.sub.5, R.sub.2O, RO and nucleating agents.
[0086] According to some embodiments of the glass-ceramic provided according to the present invention, it is substantially free of a glass component or two or more glass components selected from the group consisting of PbO, B.sub.2O.sub.3, CrO.sub.3, F, and Cd compounds.
[0087] According to the invention, the expression X-free or free of a component X means that the glass-ceramic substantially does not contain this component X, i.e. that such a component is present at most as an impurity in the glass, but is not added to the composition as an individual component. For other glass components, higher impurity contents of up to not more than 0.1 mol %, optionally not more than 0.05 mol %, optionally not more than 0.01 mol %, optionally not more than 0.005 mol %, for certain components optionally not more than 0.003 mol %, based in each case on one component, may be possible. X here represents any component, for example PbO.
[0088] The glass-ceramics provided according to the invention comprise high quartz solid solution as the main crystal phase. The main crystal phase is the crystalline phase having the greatest vol % fraction in the crystal phase. High quartz solid solution is a metastable phase which, depending on the crystallization conditions, changes its composition and/or structure or is transformed into a different crystal phase. The high quartz-containing solid solutions have very low thermal expansion or even falling thermal expansion with rising temperature. In some embodiments, the crystal phase contains no ?-spodumene and no keatite.
[0089] Some embodiments of the LAS glass-ceramic have a crystal phase fraction of less than 75 vol % and/or advantageously more than 45 vol %. The crystal phase consists of high quartz solid solution, which is also called ?-eucryptite solid solution. The average crystallite size of the high quartz solid solution may be <100 nm, optionally <80 nm, optionally <70 nm. The effect of the small crystallite size is that the glass-ceramic is transparent and can also be more effectively polished. In some embodiments, the average crystallite size of the high quartz solid solution may be ?60 nm, optionally <50 nm. The crystal phase, its fraction and the average crystallite size are determined in a known manner by x-ray diffraction analysis.
[0090] According to some embodiments provided according to the present invention, a transparent glass-ceramic is produced. The transparency allows numerous properties of such a glass-ceramic to be assessed more effectively, in particular, of course, the internal quality of the glass-ceramic. The glass-ceramics provided according to the invention are transparent, meaning that they have an internal transmission of at least 70% in the wavelength range from 350 to 650 nm. B.sub.2O.sub.3 and/or relatively high fluorine contents may reduce the transparency. Some embodiments therefore do not contain one or both of the stated components. Additionally, the glass-ceramics produced in the context of the invention are pore-free and crack-free. In the context of the invention, pore-free means a porosity of less than 1%, optionally less than 0.5%, optionally of less than 0.1%. A crack is a gap, i.e. discontinuity, in an otherwise continuous structure.
[0091] In order to enable the manufacture of a homogeneous glass-ceramic in industrial-scale production plant, it may be advantageous if the processing temperature Va or the T4 value of the parent green glass of the glass-ceramic is not more than 1330? C., optionally not more than 1320? C. Some embodiments may have a processing temperature of not more than 1310? C. or not more than 1300? C. or less than 1300? C. The processing temperature Va is the temperature at which the melt has a viscosity of 10.sup.4 dPas. Homogeneity relates in particular to the homogeneity of the CTE of the glass-ceramic over a large volume, and also a small number of, optionally freedom from, inclusions such as bubbles and particles. This is a quality feature of the glass-ceramic and a prerequisite for use in precision components, especially in very large precision components.
[0092] It may additionally be advantageous if the T3 value of the parent green glass of the glass-ceramic is not more than 1550? C., optionally not more than 1525? C. and optionally not more than 1500? C. Some embodiments, indeed, have T3 values of not more than 1490? C. or not more than 1450? C. When the values are situated in this range, the green glass has good meltability and homogenizability.
[0093] The processing temperature is determined by the composition of the glass-ceramic. Since the glass network-forming SiO.sub.2 component in particular is regarded for the purpose of increasing the viscosity and hence the processing temperature, the maximum SiO.sub.2 content should be selected in line with the stipulations mentioned above. Moreover, the alkali metal oxide content and the total MgO+ZnO content lower the viscosity of the melt, causing the processing temperature to fall. This leads to an improvement in the homogeneity of the melt and hence of the green glass body generated, and of a glass-ceramic resulting from them.
[0094] CTE
[0095] The glass-ceramics provided according to the invention have zero expansion (see Table 1), meaning that they have an average coefficient of thermal expansion CTE in the range from 0 to 50? C. of at most 0?0.1?10.sup.?6/K. Some embodiments even have an average CTE in the range from 0 to 50? C. of at most 0?0.05?10.sup.?6/K. For particular applications it may be advantageous if the average CTE over a wider temperature range, for example in the range from ?30? C. to +70? C., optionally in the range from ?40? C. to +80? C., is at most 0?0.1?10.sup.?6/K, i.e. if there is zero expansion.
[0096] For the determination of the CTE-T curve of the glass-ceramics and precision components provided according to the invention and of the comparative examples, the differential CTE(T) is first determined. The differential CTE(T) is determined as a function of the temperature. The CTE is then defined according to the following formula (1):
CTE (T)=(1/l.sub.0)?(?1/?T)(1)
[0097] To create a ?l/l.sub.0?T curve or an expansion curve or plot of the change in length ?l/l.sub.0 of a test specimen (glass-ceramic or precision component) against the temperature, it is possible to measure the temperature-dependent change in length of the length of a test specimen from the starting length l.sub.0 at the starting temperature t.sub.0 to the length l.sub.t at the temperature t. Temperature intervals chosen in this case are optionally small, being for example 5? C. or 3? C. or 1? C., for the determination of a measurement point. Such measurements may be conducted, for example, by dilatometric methods, interferometric methods, for example the Fabry-P?rot method, i.e. the evaluation of the shift in the resonance peak of a laser beam injected into the material, or other suitable methods. In the context of the invention, the dilatometric method has been chosen, with a temperature interval of 1? C. on rod-shaped samples of the test specimens with length 100 mm and a diameter of 6 mm for the purpose of ascertaining the CTE. The chosen method of determining the CTE has an accuracy of optionally at least ?0.05 ppm/K, optionally of at least ?0.03 ppm/K. Of course, however, the CTE may also be determined by methods which have an accuracy of at least ?0.01 ppm/K, optionally at least ?0.005 ppm/K or, according to certain embodiments, even of at least ?0.003 ppm/K or at least ?0.001 ppm/K.
[0098] The ?l/l.sub.0?T curve is used to calculate the average CTE for a particular temperature interval, for example for the temperature range from 0? C. to 50? C.
[0099] A CTE-T curve is obtained through the derivative of the ?l/l.sub.0?T curve. The CTE-T curve can be used to determine the zero crossing, the slope of the CTE-T curve within a temperature interval. The CTE-T curve is used to determine the shape and position of an advantageous CTE plateau formed in certain variants (see below and
[0100] One exemplary configuration of a precision component comprising a glass-ceramic provided according to the invention (especially in the form of a substrate) has a high CTE homogeneity. The value of CTE homogeneity (total spatial variation of CTE) is understood here as what is called the peak-to-valley value, i.e. the difference between the respectively highest and lowest CTE values of the samples taken from a precision component. The CTE homogeneity is therefore based not on the CTE of the material of the component but rather on the spatial variation of the CTE over the section under consideration or the entire precision component. For determining the CTE homogeneity, a multiplicity of samples are taken from different sites in a precision component and the CTE value is determined for each of them, reported in ppb/K, where 1 ppb/K=0.001?10.sup.?6/K. The CTE homogeneity, i.e. the spatial variation of the CTE, over the entire precision component is optionally at most 5 ppb/K, optionally at most 4 ppb/K, optionally at most 3 ppb/K. A method for ascertaining the CTE homogeneity and measures for achieving the CTE homogeneity are described in WO 2015/124710 A, the disclosure content of which is incorporated in full into this application.
[0101] Thermal Hysteresis
[0102] In the context of the invention, the glass-ceramic, at least in the temperature range from 15? C. to 35? C., has a thermal hysteresis of <0.1 ppm and is therefore hysteresis-free (see
[0103] Thermal hysteresis of <0.1 ppm at least in the temperature interval from 15? C. to 35? C. therefore means that within this temperature interval, after a thermal treatment and subsequent holding at constant temperature, the glass-ceramic has a change in length of <0.1 ppm, based on a heating rate or cooling rate of 36 K/h, i.e. 0.6 K/min, and a hold time of 5 hours at ?10? C. The feature of thermal hysteresis therefore describes the thermal characteristics of the glass-ceramic or of a component manufactured from it, over time.
[0104] In some embodiments, this freedom from hysteresis is present at least in a temperature range from 15 to 40? C. or at least in the temperature range of 10? C. to 35? C., optionally at least in the temperature range of 15 to 45? C., optionally at least in the temperature range of 15? C. to 50? C. In some embodiments, the temperature range of the freedom from hysteresis is even wider, and so the material or the component is also suitable for applications at temperatures of up to at least 100? C. and above as well. In some embodiments, the temperature range of the freedom from hysteresis is even wider. Exemplary application temperatures are in the ?60 to 100? C. range, optionally from ?40? C. to +80? C. Some variants provided according to the present invention relate to glass-ceramics and precision components for application temperatures T.sub.A for example in the range of 5? C. to 20? C. or T.sub.A of 22? C., 40? C., 60? C., 80? C. and 100? C., which are optionally hysteresis-free at these temperatures as well.
[0105] The thermal hysteresis was determined for the glass-ceramics and precision components provided according to the invention and for the comparative examples using a precision dilatometer capable of ascertaining the CTE with a reproducibility of ?0.001 ppm/K and ?0.003 ppm/K absolutely, with a temperature interval of 1? C., on rod-shaped samples of length 100 mm and a diameter of 6 mm of the test specimens (i.e. sample of the precision component or sample of the glass-ceramic), in accordance with the method and apparatus construction disclosed in DE 10 2015 113 548 A, the disclosure content of which is incorporated in full into this application. For each sample analysed, the change in length ?l/l.sub.0 was determined as a function of the temperature between 50? C., cooling at a cooling rate of 36 K/h, to ?10? C.
[0106] After an isothermal hold time of 5 hours at ?10? C., the sample was heated at a heating rate of 36 K/h to 50? C. and the change in length ?l/l.sub.0 was recorded as a function of the temperature. The thermal hysteresis characteristics of a test specimen are considered at ?5? C., 0? C., 5? C., 10? C., 15? C., 19? C., 22? C., 35? C. and 40? C. These points are representative of the temperature range from ?10? C. to 50? C., since hysteresis decreases with rising temperature within the temperature interval stated. Hence a sample which is hysteresis-free at 22? C. or 35? C. also shows no hysteresis in the range up to 50? C.
[0107] For determining the thermal hysteresis at 15? C., the individual measurement values of the change in length for the five temperatures of 13? C., 14? C., 15? C., 16? C. and 17? C., i.e. two temperature points above and two temperature points below 15? C., were recorded both during heating and during cooling of the sample in the range of ?10? C. to 50? C. at the rate of 36 K/h. The differences in the measurement values for heating curve and cooling curve at these five measurement points were used to form the average, which is listed as Hyst.@15? C. in the unit [ppm] in the tables.
[0108] For determining the thermal hysteresis at 35? C., correspondingly, the individual measurement values of the change in length for the five temperatures of 33? C., 34? C., 35? C., 36? C. and 37? C., i.e. two temperature points above and two temperature points below 35? C., were recorded both during heating and during cooling of the sample in the range of ?10? C. to 50? C. at the rate of 36 K/h. The differences in the measurement values for heating curve and cooling curve at these five measurement points were used to form the average, which is listed as Hyst.@35? C. in the unit [ppm] in the tables.
[0109] Corresponding procedures were adopted for the other temperature points referred to above.
[0110]
[0111]
[0112] The LAS glass-ceramics analysed that are represented in
[0113] LAS glass-ceramics and precision components provided according to the invention have a defined content of the sum total of MgO+ZnO of >0.5 mol % to 1.5 mol % in combination with a defined R.sub.2O content of more than 0.5 mol %. As is apparent from
[0114] Further Expansion Properties
[0115] Some embodiments provided according to the invention may have further advantageous expansion features:
[0116] For describing the expansion characteristics of a test specimen (glass-ceramic or precision component), a TCL value is frequently reported, with TCL meaning total change of length. Within the context of the invention, the TCL value is reported for the temperature range of 0? C. and 50? C. It is ascertained from the normalized ?l/l.sub.0?T curve (also dl/l.sub.0?T curve in the FIGS.) of the respective test specimen, with normalized meaning that the change in length at 0? C. is 0 ppm. The ?l/l.sub.0?T curve for determining the TCL is created by the same method as described above in connection with the determination of CTE in the context of the invention.
[0117] The TCL value is the distance between the highest di/l.sub.0 value and the lowest dl/l.sub.0 value within this temperature range:
TCL (0;50? C.)=|dl/l.sub.0 max.|+|dl/l.sub.0 min.|(2)
where dl denotes the change in length at the respective temperature and l.sub.0 denotes the length of the test specimen at 0? C. The calculation is based in each case on the magnitudes of the dl/l.sub.0 values.
[0118]
[0119] In the context of the present invention, by contrast, a flat profile of the expansion curve in the temperature range of 0? C. to 50? C. is an advantageous feature of the glass-ceramic and of a precision component (see
[0120] As a statement as to the extent to which the curve profile of the thermal expansion differs from a simple linear profile, for some embodiments provided according to the invention the index F is introduced as a measure of the flatness of the expansion curve, so enabling a classification of CTE curves:
F=TCL (0;50? C.)|expansion (0;50? C.)|(3)
[0121] The index F is calculated by forming the quotient of the TCL (0;50) value [in ppm](see above) and the difference in expansion between the temperature points of 0? C. and 50? C. [in ppm]. Since the expansion curve for determining the TCL is by definition normalized in such a way that the change in length at 0? C. is 0 ppm, the difference in expansion between the temperature points at 0? C. and 50? C. corresponds to the expansion at 50? C., as indicated in the tables. The index F is calculated using the magnitude of the expansion at 50? C.
[0122] It may be advantageous here if for the respective material or component, the index F is <1.20, optionally <1.15, optionally <1.10, optionally at most 1.05. The closer the index F is to 1, the flatter the expansion curve.
[0123] It is apparent from
[0124]
[0125] Some glass-ceramics and precision components provided according to the invention therefore have a very flat profile of their expansion curves, in the temperature range from 0? C. to 50? C., for example, meaning that in the temperature range under consideration they not only have zero expansion but also exhibit a low fluctuation in the change in lengthwise expansion and hence in the differential CTE in this range. As is apparent, for example, from
[0126] In comparison to the exemplary embodiments of the glass-ceramics and precision components provided according to the invention,
[0127]
[0128] The index F is calculated correspondingly for a known LAS glass-ceramic and a corresponding precision component (see
[0129] The index F is calculated correspondingly for a known cordierite glass-ceramic and a corresponding precision component (see
[0130] The index F is calculated correspondingly for a known sintered cordierite ceramic and a corresponding precision component (see
[0131] Glass-ceramics with a flat profile of the expansion curves can be very advantageous, since it is then possible not just to optimize a precision component for the subsequent application temperature but also for it to have likewise low thermal expansion, for example, under relatively high and/or relatively low temperature loads, during production, for example. Precision components for microlithography, EUV microlithography (also EUV lithography or EUVL for short) and metrology are typically used under standard cleanroom conditions, in particular a room temperature of 22? C. The CTE may be matched to this application temperature. However, such components are subjected to various process steps, such as coating with metallic layers, and cleaning, structuring and/or exposure operations, for example, in which temperatures may be higher or in some cases lower than those prevailing in the case of subsequent use in a cleanroom. Glass-ceramics and precision components manufactured from them that have an index F of <1.20 and hence optimized zero expansion not just at application temperature but also at possibly higher and/or lower temperatures during production are therefore very advantageous. Properties such as freedom from hysteresis and an index F<1.20 may be particularly advantageous if the precision component or a glass-ceramic is used in EUV lithography, i.e. if, for example, the precision component is an EUVL mirror or EUVL mask blank or a corresponding substrate therefor, since the mirrors or masks in particular in EUV lithography become heated very nonuniformly at different points or in beam direction as a result of being irradiated with high-energy radiation. For such usage conditions, it is advantageous if the precision component or glass-ceramic exhibits a low slope of the CTE-T curve in a temperature range around the application temperature (see below).
[0132] A feature of glass-ceramics and precision components that are even better optimized to a later application temperature at 20 or 22? C. is that they have a relative change in length (dl/l.sub.0) of ?|0.10| ppm, optionally of <|0.09| ppm, optionally of <|0.08| ppm and optionally of 10.071 ppm in the temperature range from 20? C. to 30? C. and/or a relative change in length (dl/l.sub.0) of <|0.17| ppm, optionally of |0.15| ppm, optionally of |0.13| ppm and optionally of ?|0.11| ppm in the temperature range from 20? C. to 35? C.
[0133] Alternatively or additionally, a feature of such optimized glass-ceramics and precision components may be that they have a relative change in length (dl/l.sub.0) of ?|0.30| ppm, optionally of ?|0.25| ppm, optionally of ?10.201 ppm and optionally of ?|0.15| ppm in the temperature range from 20? C. to 40? C. The features relating to the relative change in length based on the different temperature intervals may optionally be taken from the dl/l.sub.0 curves of
[0134] A zero-expansion, hysteresis-free material having such advantageous expansion characteristics is particularly suitable for use as a substrate for an EUVL mirror or as an EUVL mirror which is heated to different degrees in operation, as a result for example of the respective exposure mask, in regions of light and shadow. On account of the above-stated low relative change in length, an EUVL mirror formed from the advantageous glass-ceramic has relatively low local gradients (or local slopes) in the topography of the mirror surface than an EUVL mirror manufactured using known materials. The same is applicable, analogously, to EUVL mask blanks or EUVL masks or EUVL photomasks.
[0135] Particularly in the case of a glass-ceramic which within the temperature range under consideration exhibits a very flat profile of the expansion curve, which is close to 0 ppm or fluctuates around 0 ppmwhich constitutes advantageous expansion characteristics overallit may be advantageous, alternatively or additionally to the index F, to introduce a further measure of the flatness of the expansion curve, in which the expansion curve is considered not in the temperature range of (0;50), but instead in a different temperature interval (T.i.), optionally in the temperature range of (20;40), (20;70) and/or (?10; 30). This allows the expansion characteristics to be classified in relation to the later fields of application.
[0136] The alternative index f.sub.T.i. has the unit (ppm/K) and is defined as:
f.sub.T.i.=TCL.sub.(T.i.)/width of the temperature interval (T.i.)(4)
where T.i. describes the temperature interval under consideration in each case.
[0137] The TCL.sub.(T.i) value is the distance between the highest dl/l.sub.0 value and the lowest dl/l.sub.0 value within the temperature range (T.i.) under consideration in each case, where the expansion curve for the determination of TCL.sub.(T.i.) as well is by definition normalized in such a way that the change in length at 0? C. is 0 ppm. In other words, for example:
TCL.sub.(20;40? C.)=|dl/l.sub.0 max.|+|dl/l.sub.0 min.|(5)
where dl denotes the change in length at the respective temperature and l.sub.0 denotes the length of the test specimen at 0? C. The calculation is based in each case on the magnitudes of the dl/l.sub.0 values when the curve fluctuates around zero in the temperature interval under consideration (e.g.
[0138] Otherwise, the TCL.sub.(T.i.) is the distance ascertained from the difference between the highest dl/l.sub.0 value and the lowest dl/l.sub.0 value within the temperature interval (T.i.) under consideration in each case, this being self-evident and apparent from the FIGS. (e.g.
TCL.sub.(T.i.)=dl/l.sub.0 max.?dl/l.sub.0 min.(6)
[0139] The alternative index f.sub.T.i. is calculated according to formula (4) by forming the quotient from the TCL.sub.(T.i.) value [in ppm] (see above) and the width of the temperature interval (T.i.) reported in [K] in which the difference in expansion is being considered. The width of the temperature interval considered between 20? C. and 40? C. is 20K. If, in contrast, the profile of the expansion curve is considered in the interval T.i.=(20;70) or (?10;30), the divisor for formula (4) is 50K or 40K, respectively.
[0140] In some embodiments, the glass-ceramic has an alternative index f.sub.(20;40)<0.024 ppm/K and/or an alternative index f.sub.(20;70)<0.039 ppm/K and/or an alternative index f.sub.(?10;30)<0.015 ppm/K.
[0141] Glass-ceramics having a very flat profile of the expansion curves may be very advantageous, since it is then possible to optimize a precision component not only for the later application temperature but also, for example, for higher and/or lower temperature loads that can be expected. The alternative index f.sub.T.i. is suitable for defining a suitable material in accordance with the specifications required for particular component applications, and for providing a corresponding precision component. Specific precision components and their applications are described later on below and are included here as well.
[0142] According to some embodiments of the glass-ceramic or a component produced from it, it may be advantageous if the alternative index f.sub.(20;40) is <0.024 ppm/K, optionally <0.020 ppm/K, optionally <0.015 ppm/K. A hysteresis-free, zero-expansion component having such expansion characteristics in the temperature range of (20;40) has particularly good usability as a precision component for microlithography and EUV microlithography at room temperature. One example of a glass-ceramic of this kind is represented in
[0143] According to some embodiments of the glass-ceramic or a component produced from it, it may be advantageous if the alternative index f.sub.(20;70) is <0.039 ppm/K, optionally <0.035 ppm/K, optionally <0.030 ppm/K, optionally <0.025 ppm/K, optionally <0.020 ppm/K. A hysteresis-free, zero-expansion component having such expansion characteristics in the temperature range of (20;70) likewise has particularly good usability as a precision component for microlithography and EUV microlithography. It may be advantageous if the component has an equally low thermal expansion at higher temperature loads as well, as may occur, for example, during the production of the precision component, but also locally or over an area in operation. Further details of the temperature loads that occur in the context of EUVL precision components have already been described above in connection with the index F, to which reference is made here for avoidance of repetitions. One example of a glass-ceramic of this kind is represented in
[0144] According to some embodiments of the glass-ceramic or a component produced from it, it may be advantageous if the alternative index f.sub.(?10;30) is <0.015 ppm/K, optionally <0.013 ppm/K, optionally <0.011 ppm/K. A hysteresis-free, zero-expansion component having such expansion characteristics in the temperature range of (?10;30) has particularly good usability as a precision component, more particularly as mirror substrates for applications in which temperatures lower than room temperature are among those which may occur; for example, as mirror substrates in astronomy or in Earth observation from space. Corresponding components are described later on below. One example of a glass-ceramic of this kind is represented in
[0145] One exemplary embodiment of a glass-ceramic or a component produced from it has an expansion curve for which at least 2 of the alternative indices f.sub.(T.i.) are applicable.
[0146] One exemplary embodiment of a glass-ceramic or a component produced from it has an expansion curve for which the index F and at least one of the alternative indices f.sub.(T.i.) are applicable.
[0147]
[0148] It may be advantageous if the differential CTE has a plateau close to 0 ppm/K, meaning that the differential CTE in a temperature interval T.sub.P having a width of at least 40 K, optionally at least 50 K, is less than 0?0.025 ppm/K. The temperature interval of the CTE plateau is defined as T.sub.P. Optionally, the differential CTE in a temperature interval T.sub.P having a width of at least 30 K or at least 40 K may be less than 0?0.015 ppm/K.
[0149] A CTE plateau is thus understood to mean a region extending over a section of the CTE-T curve, in which the differential CTE does not exceed a value of 0?0.025 ppm/K, optionally 0?0.015 ppm/K, optionally 0?0.010 ppm/K, optionally 0?0.005 ppm/K, i.e. a CTE close to 0 ppb/K.
[0150] Optionally, the differential CTE in a temperature interval T.sub.P having a width of at least 30 K or at least 40 K may be less than 0?0.015 ppm/K, i.e. 0?15 ppb/K. In some embodiments, a CTE plateau of 0?0.01 ppm/K, i.e. 0?10 ppb/K, may be formed over a temperature interval of at least 20 K or at least 30 K or at least 40 or at least 50 K. In
[0151] It may be advantageous if the temperature interval T.sub.P is in a range from ?10 to +100? C., optionally 0 to 80? C.
[0152] The position of the CTE plateau of the glass-ceramic is optionally matched to the application temperature T.sub.A of the precision component. Exemplary application temperatures T.sub.A are in the range of ?60? C. to +100? C., optionally from ?40? C. to +80? C. Particular variants of the present invention relate to precision component and glass-ceramics for application temperatures T.sub.A of 0? C., 5? C., 10? C., 22? C., 40? C., 60? C., 80? C. and 100? C. The CTE plateau, i.e. the region of the curve that has the low deviation of the differential CTE in the temperature interval T.sub.y, may also be situated in the temperature range of [?10;100]; [0;80], [0; 30? C.], [10; 40? C.], [20; 50? C.], [30; 60? C.], [40; 70? C.] and/or [50; 80? C.]. In some glass-ceramics and precision components, the CTE plateau may also be situated in the temperature range of [?10;30], [0;50], [19:25? C.]; [20;40] and/or [20;70].
[0153] According to some embodiments provided according to the invention, the CTE-T curve of the glass-ceramic or precision component in a temperature interval which has at least a width of 30 K, optionally at least a width of 40 K, optionally at least a width of 50 K, has at least one section of curve with low slope, more particularly a slope of at most 0?2.5 ppb/K.sup.2, optionally of at most 0?2 ppb/K.sup.2, optionally of at most 0?1.5 ppb/K.sup.2, optionally of at most 0?1 ppb/K.sup.2, optionally of at most 0?0.8 ppb/K.sup.2, and even, according to some variants, of at most 0?0.5 ppb/K.sup.2.
[0154] The temperature interval with low slope is optionally adapted to the application temperature T.sub.A of the precision component. Exemplary application temperatures T.sub.A are in the range of ?60? C. to +100? C., optionally of ?40? C. to +80? C. Some variants of the present invention relate to glass-ceramics and precision component for application temperatures T.sub.A of 0? C., 5? C., 10? C., 22? C., 40? C., 60? C., 80? C. and 100? C. The temperature interval with low slope may also be situated in the temperature range of [?10;100], [0;80], [0; 30? C.], [10; 40? C.], [20; 50? C.], [30; 60? C.], [40; 70? C.] and/or [50; 80? C.]. In further exemplary glass-ceramics and precision components, the temperature interval with low slope may also be situated in the temperature range of [?10;30], [0;50], [19:25? C.], [20;40] and/or [20;70].
[0155]
[0156] Glass-ceramics and precision components having such expansion characteristics are especially readily suitable for EUV lithography applications (e.g. as mirrors or substrates for mirrors or masks or mask blanks), since in this range the requirements with regard to the materials and precision components used for the optical components are becoming increasingly high in relation to extremely low thermal expansion, a zero crossing of the CTE-T curve close to the application temperature, and, in particular, to a low slope of the CTE-T curve. In the context of the invention, some advantageous configurations of a glass-ceramic or precision component have a very flat CTE profile, with the profile exhibiting not only a zero crossing but also a very low CTE slope and possibly a very flat plateau.
[0157] The feature of the low slope may be present with or without development of an advantageous CTE plateau.
[0158] By varying the ceramization temperature and/or ceramization time, it is possible to adapt the expansion curves and/or the CTE profile to different application temperatures. For example, the zero crossing of the CTE-T curve may thus be shifted by raising or lowering the ceramization temperature, or the expansion curve can be adjusted. Alternatively, for increasing or lowering the ceramization temperature, it is also possible to respectively extend or shorten the ceramization time correspondingly.
[0159] Some advantageous glass-ceramics and precision components additionally have good internal quality. They optionally have at most 5 inclusions per 100 cm.sup.3, optionally at most 3 inclusions per 100 cm.sup.3, optionally at most 1 inclusion per 100 cm.sup.3. Inclusions are understood in accordance with the invention to refer both to bubbles and to crystallites having a diameter of more than 0.3 mm.
[0160] According to some embodiments, precision components are provided which have a diameter or an edge length of at most 800 mm and a thickness of at most 100 mm and have at most 5, optionally at most 3, optionally at most 1 inclusion(s), in each case per 100 cm.sup.3, having a diameter of a size of more than 0.03 mm.
[0161] As well as the number of inclusions, the maximum diameter of the inclusions detected also serves as a measure of the level of the internal quality. The maximum diameter of individual inclusions within the total volume of a precision component having a diameter of less than 500 mm or edge lengths of less than 500 mm is optionally at most 0.6 mm, in the critical volume for the application, for example close to the surface, optionally at most 0.4 mm. The maximum diameter of individual inclusions in glass-ceramic components having a diameter of 500 mm to less than 2 m or edge lengths of 500 mm to less than 2 m is optionally at most 3 mm, in the volume critical for the application, for example close to the surface, optionally at most 1 mm. This may be advantageous in order to achieve the surface quality needed for the application.
[0162] The invention relates further to the use of a glass-ceramic provided according to the invention in a precision component. The glass-ceramic may, for example, form a substrate for the precision component.
[0163] Further, the invention relates to the use of an LAS glass-ceramic provided according to the invention in a precision component more particularly for use in metrology, spectroscopy, measurement technology, lithography, astronomy or Earth observation from space, for example as mirror or mirror carrier for segmented or monolithic astronomical telescopes or else as weight-reduced or ultra-light mirror substrates for, for example, space-based telescopes or as high-precision structure components for measurement of distance, for example in space, or optics for Earth observation, as precision components, such as standards for precision measurement technology, precision rules, reference plates in interferometers, as mechanical precision parts, for example for ring laser gyroscopes, spiral springs for the clock industry, as for example mirrors and prisms in LCD lithography, and for example as mask holders, wafer stages, reference plates, reference frames and grid plates in microlithography and in EUV (extreme UV) microlithography, and additionally as mirrors or mirror substrates and/or photomask substrates or photomask blanks or reticle mask blanks in EUV microlithography.
[0164] A glass-ceramic provided according to the invention may be used to produce precision components in different sizes:
[0165] Some embodiments relate to precision components having relatively small dimensions, more particularly in the case of (rect)angular shapes with edge lengths (width and/or depth) or in the case of round areas having diameters of at least 50 mm, optionally at least 100 mm and/or not more than 1500 mm, optionally not more than 1000 mm and/or a thickness of less than 50 mm, optionally less than 10 mm and/or at least 1 mm, optionally at least 2 mm. Such precision components may be employed, for example, in microlithography and EUV lithography.
[0166] Some embodiments concern precision components having very small dimensions, more particularly having edge lengths (width and/or depth) or diameters and/or thickness of a few mm (for example at most 20 mm or at most 10 mm or at most 5 mm or at most 2 mm or at most 1 mm) to a few tenths of a mm (for example at most 0.7 mm or at most 0.5 mm). These precision elements may be, for example, a spacer, for example in an interferometer, or a component for ultra-stable clocks in quantum technology.
[0167] It is alternatively possible to produce very large precision components. Some embodiments provided according to the invention thus relate to components of high volume. In the context of this application, this term is taken to mean a component having a mass of at least 300 kg, optionally at least 400 kg, optionally at least 500 kg, optionally at least 1 t, optionally at least 2 t, according to some variants provided according to the invention at least 5 t, and/or having edge lengths (width and/or depth) in the case of (rect)angular shapes of at least 0.5 m, optionally at least 1 m, and/or with a thickness (height) of at least 50 mm, optionally at least 100 mm, optionally at least 200 mm, optionally at least 250 mm, or, in the case of round shapes, having a diameter of at least 0.5 m, optionally at least 1 m, optionally at least 1.5 m and/or having a thickness (height) of at least 50 mm, optionally at least 100 mm, optionally at least 200 mm, optionally at least 250 mm.
[0168] Some embodiments provided according to the invention may also be even larger components, having, for example, a diameter of at least 3 m or at least 4 m or greater and/or a thickness of 50 mm to 400 mm, optionally 50 mm to 300 mm. According to some embodiments, the invention also relates to rectangular components, where optionally at least one surface has an area of at least 1 m.sup.2, optionally at least 1.2 m.sup.2, optionally at least 1.4 m.sup.2, for certain variants optionally at least 3 m.sup.2 or at least 4 m.sup.2, and/or the thickness is 50 mm to 400 mm, optionally 50 mm to 300 mm. Generally speaking, large-volume components are produced that have a significantly greater base area than height. However, the large-volume components in question may also be those which have a shape approximated to a cube or a sphere.
[0169] Precision components may be, for example, optical components, specifically what is called a normal-incidence mirror, i.e. a mirror which is operated close to the perpendicular impingement of radiation, or what is called a grazing-incidence mirror, i.e. a mirror which is operated at the grazing impingement of radiation. Such a mirror comprises not only the substrate but also a coating that reflects the incident radiation. Especially in the case of a mirror for x-radiation, the reflective coating is, for example, a multilayer system or multilayer having a multiplicity of layers of high reflectivity in the x-ray range in the case of non-grazing incidence. A multilayer system of this kind for a normal-incidence mirror optionally comprises 40 to 200 pairs of layers, consisting of alternating layers of, for example, one of the material pairings Mo/Si, Mo/Bi, Ru/Si and/or MoRu/Be.
[0170] In particular, the optical elements provided according to the invention may be x-ray-optical elements, i.e. optical elements that are used in conjunction with x-radiation, more particularly soft x-radiation or EUV radiation, and more particularly photomasks or reticle masks that are operated in reflection, especially for EUV microlithography. This may be mask blanks. With further advantage, the precision component can be used as a mirror for EUV lithography or as a substrate for a mirror for EUV lithography.
[0171] The precision component provided according to the invention may further be a component, especially a mirror, for astronomical applications. Such components for use in astronomy may be employed here either terrestrially or in space. High-precision structure components for measurements of distance, in space for example, are a further advantageous field of application.
[0172] The precision component provided according to the invention may be a lightweight structure. The component provided according to the invention may further comprise a lightweight structure. This means that in certain regions of the component, cavities are provided for reducing the weight. As a result of lightweight working, the weight of a component is reduced optionally by at least 80%, optionally at least 90%, by comparison with the unworked component.
[0173] A further subject provided according to the invention is a precision component which comprises an LAS glass-ceramic provided according to the invention. Details in this regard have already been described above in connection with the glass-ceramic and the use thereof in precision components. This disclosure is incorporated fully into the description of the precision component.
[0174] It will be appreciated that the features provided according to the invention that have been stated above and those still to be elucidated hereinafter can be used not only in the combination specified in each case but also in other combinations without leaving the scope of the invention.
Examples
[0175] Tables 1 and 2 show compositions of examples of glass-ceramics provided according to the invention and compositions of comparative examples, and their properties.
[0176] The compositions stated in Table 1 were melted from commercial raw materials, such as oxides, carbonates and nitrates in customary production processes. The green glasses produced according to Table 1 were first ceramized at the maximum temperature specified in each case, over the specific time.
[0177] The production of a glass-ceramic for a precision component, more particularly a large precision component, is described for example in WO 2015/124710 A1.
[0178] Table 1 shows 4 examples (Ex.) provided according to the invention which are hysteresis-free at least in a temperature range of 15? C. to 35? C. and have zero expansion. Examples 1 to 4 exhibit thermal hysteresis below around 15? C. Moreover, the index F is <1.20, i.e. the profile of the expansion curve in the temperature range of 0? C. to 50? C. is advantageously flat for all the examples. Furthermore, the examples have a processing temperature <1330? C., allowing the glass-ceramics to be produced with high homogeneity in industrial-scale production plants. The processing temperatures as reported in Tables 1 and 2 were ascertained in accordance with DIN ISO 7884-1 (2014source: Schott Techn. Glas-Katalog).
[0179] In the case of example 1, after ceramization at not more than 815? C. over the time of 2.5 days, the average CTE was determined for further temperature intervals, with the following result: CTE (20; 300? C.): 0.39 ppm/K, CTE (20; 500? C.): 0.68 ppm/K, CTE (20; 700? C.): 0.94 ppm/K.
[0180] Table 2 shows comparative examples (Comp. Ex.). Comparative examples 1 and 2 contain neither MgO nor ZnO, but the average CTE(0;50) is greater than 0?0.1?10.sup.?6/K, i.e. these comparative examples do not have zero expansion. Furthermore, comparative examples 1 and 2 have a processing temperature >1330? C. These materials are very viscous, and so it is not possible to use them to manufacture components of high homogeneity in industrial-scale production plants.
[0181] Comparative examples 3 and 7 to 16 all contain MgO and/or ZnO, and most of them have zero expansion. However, these comparative examples, at least in the temperature range of 15? C. to 35? C., exhibit a thermal hysteresis of substantially more than 0.1 ppm. At room temperature, i.e. 22? C., this group of comparative examples has thermal hysteresis, except for comparative examples 14 and 16. Comparative example 9, although it has zero expansion, additionally has an unadvantageously steep profile of the expansion curve in the temperature range of 0? C. to 50? C., as evident from the high value for the index F. Comparative example 3 features a comparatively low sum total of MgO+ZnO, but contains no R.sub.2O. In the 15? C. to 35? C. temperature range at least it has a thermal hysteresis of substantially more than 0.1 ppm. Moreover, the expansion curve is sharply curved, as evident from the high value for the index F.
[0182] Empty fields in the tables below for the details concerning the composition mean that this/these component(s) was/were not added deliberately or is/are not present.
[0183] For two examples provided according to the invention and one comparative example, Table 3 shows the calculated alternative index f.sub.(T.i.) for different temperature intervals, from which it is apparent that the expansion curves of the examples in the temperature ranges defined each have a flatter profile than the comparative example.
[0184] It will be clear to experts thatdepending on the application temperature of the glass-ceramic or of the precision component comprising the glass-ceramicthe glass-ceramic chosen is one having the desired properties, especially in terms of the thermal hysteresis and/or average CTE.
TABLE-US-00006 TABLE 1 Compositions, ceramization and properties (mol %) Example No. (Ex.) 1 2 3 4 Li.sub.2O 8.7 9.3 9.35 8.1 Na.sub.2O 0.30 0.75 0.60 0.30 K.sub.2O 1.00 0.45 1.20 0.45 MgO 0.75 0.55 0.30 ZnO 0.70 0.30 0.50 CaO 1.60 1.25 2.10 BaO 0.55 0.2 SrO 0.2 Al.sub.2O.sub.3 17.0 18.5 14.7 15.2 SiO.sub.2 67.15 62.5 67.1 68.15 P.sub.2O.sub.5 3.4 3.0 1.55 TiO.sub.2 1.85 1.9 2.0 1.85 ZrO.sub.2 0.95 1.0 1.0 0.9 Sb.sub.2O.sub.3 0.2 0.2 As.sub.2O.sub.3 0.2 0.2 Total 100.0 100.0 100.0 100.0 SiO.sub.2 + (5xLi.sub.2O) 110.65 109.00 113.85 108.70 MgO + ZnO 0.70 0.75 0.85 0.80 ?R.sub.2O 1.30 1.20 1.80 0.75 (R = Na, K, Cs, Rb) ?RO (R = Ca, Ba, Sr) 2.15 1.25 2.55 Va (=T4) [? C.] 1269 1307 1298 T3 [? C.] 1436 1488 1472 Ceram. temperature 815? C. 815? C. 810? C. 810? C. [? C.] Ceram. time [days] 2.5 2.5 2.5 2.5 Cryst. phase [vol %] 55 64 63 62 Cryst. size [nm] 51 55 47 44 Av. CTE(0; +50? C.) ?0.07 0.02 ?0.06 ?0.015 [ppm/K] TCL (0; +50? C.) 3.49 0.96 2.89 0.79 |Expansion at 50? C.| 3.49 0.96 2.89 0.73 Index F 1.00 1.00 1.00 1.08 Hyst @ 45? C. [ppm] <0.1 <0.1 <0.1 <0.1 Hyst @ 35? C. [ppm] <0.1 <0.1 <0.1 <0.1 Hyst @ 30? C. [ppm] <0.1 <0.1 <0.1 <0.1 Hyst @ 22? C. [ppm] <0.1 <0.1 <0.1 <0.1 Hyst @ 19? C. [ppm] <0.1 <0.1 <0.1 <0.1 Hyst @ 15? C. [ppm] <0.1 <0.1 <0.1 <0.1 Hyst @ 10? C. [ppm] 0.1 0.13 0.1 0.15 Hyst @ +5? C. [ppm] 0.13 0.20 0.11 0.25 Hyst @ 0? C. [ppm] 0.21 0.30 0.18 0.38 Ceram. temperature 815? C. 815? C. 810? C. 810? C. [? C.] Ceram. time [days] 2.5 2.5 2.5 2.5 Av. CTE ?0.10 0.004 ?0.06 ?0.03 (?30; +70? C.)[ppm/K] Av. CTE ?0.10 ?0.005 ?0.10 ?0.05 (?40; +80? C.)[ppm/K]
TABLE-US-00007 TABLE 2 Compositions, ceramization and properties (mol %) Comparative example No. (Comp. Ex.) 1 2 3 Li.sub.2O 8.1 9.15 8.15 Na.sub.2O 0.4 0.4 K.sub.2O 0.15 0.2 MgO 0.45 ZnO 0.30 CaO 4.15 2.1 BaO 0.6 0.95 SrO Al.sub.2O.sub.3 12.45 14.2 15.35 SiO2 72.3 71.7 68.15 P.sub.2O.sub.5 0.62 1.5 TiO.sub.2 1.3 1.75 1.85 ZrO.sub.2 1.0 1.2 0.95 As2O.sub.3 0.15 0.15 0.25 Total 100.0 100.0 100.0 SiO.sub.2 + (5xLi.sub.2O) 108.90 MgO + ZnO 0.75 ?R.sub.2O (R = Na, K, Cs, Rb) 0.55 0.6 0 ?RO (R = Ca, Ba, Sr) 4.15 0.6 3.05 Va [? C.] 1345 1340 1295 Ceram. temperature [? C.] 760 790? C. Ceram. time [days] 10 2.5 Cryst. phase [vol %] 60 63 Cryst. size [nm] 63 39 Av. CTE(0; +50? C.) [ppm/K] ?0.25 ?0.006 TCL (0; +50? C.) 0.62 |Expansion at 50? C.| 0.28 Index F 2.21 Hyst @ 45? C. [ppm] <0.1 Hyst @ 35? C. [ppm] <0.1 Hyst @ 30? C. [ppm] 0.11 Hyst @ 22? C. [ppm] <0.1 0.15 Hyst @ 19? C. [ppm] <0.1 Hyst @ 15? C. [ppm] <0.1 0.23 Hyst @ 10? C. [ppm] <0.1 0.33 Hyst @ +5? C. [ppm] <0.1 0.48 Hyst @ 0? C. [ppm] 0.13 Ceram. temperature [? C.] Ceram. time [days] Av. CTE (?30; +70? C.)[ppm/K] Av. CTE (?40; +80? C.)[ppm/K] Comparative example No. (Comp. Ex.) 7 8 9 10 11 12 Li.sub.2O 8.5 7.78 9.32 9.2 9.4 9.0 Na.sub.2O 0.1 0.8 0.1 0.2 0.1 K.sub.2O 0.5 MgO 1.8 1.2 1.6 1.2 1.6 ZnO 1.3 1.8 0.4 0.6 0.6 0.4 CaO 2.42 1.0 1.2 1.0 1.3 BaO 1.07 0.36 0.4 0.3 0.5 SrO Al.sub.2O.sub.3 16.9 15.39 19.11 16.2 19.0 16.4 SiO.sub.2 64.3 65.42 61.4 63.3 61.4 63.9 P.sub.2O.sub.5 3.4 2.47 3.97 3.8 3.9 3.5 TiO.sub.2 1.9 1.67 1.92 2.2 1.9 2.1 ZrO.sub.2 1.1 0.92 1.07 1.1 1.1 1.2 As.sub.2O.sub.3 0.2 0.26 0.25 0.2 0.2 0.1 Total 100.0 100.0 100.0 100.0 100.0 100.1 SiO.sub.2 + (5xLi.sub.2O) MgO + ZnO 3.1 1.8 1.6 2.2 1.8 2.0 ?R.sub.2O (R = Na, K, Cs, Rb) 0.6 0.8 0.1 0.2 0.1 ?RO (R = Ca, Ba, Sr) 3.49 1.36 1.6 1.3 1.8 Va [? C.] Ceram. temperature [? C.] 810 760 810 760 Ceram. time [days] 10 10 5 10 Cryst. phase [vol %] 76 Cryst. size [nm] 72 Av. CTE(0; +50? C.) [ppm/K] 0.03 0.02 0.002 ?0.15 0.03 ?0.05 TCL (0; +50? C.) 1.19 3.68 1.32 0.35 |Expansion at 50? C.| 0.11 3.68 1.28 0.35 Index F 10.82 1.00 1.03 1.00 Hyst @ 45? C. [ppm] 0.11 <0.1 <0.1 <0.1 <0.1 <0.1 Hyst @ 35? C. [ppm] 0.14 <0.1 0.12 <0.1 <0.1 <0.1 Hyst @ 30? C. [ppm] 0.18 <0.1 0.16 <0.1 0.1 0.11 Hyst @ 22? C. [ppm] 0.27 0.14 0.24 0.14 0.16 0.17 Hyst @ 19? C. [ppm] Hyst @ 15? C. [ppm] Hyst @ 10? C. [ppm] 0.61 0.42 0.54 0.38 0.85 0.43 Hyst @ +5? C. [ppm] 0.85 0.61 0.74 0.56 0.61 0.61 Hyst @ 0? C. [ppm] 1.1 0.81 0.92 0.76 0.85 0.82 Ceram. temperature [? C.] Ceram. time [days] Av. CTE (?30; +70? C.)[ppm/K] Av. CTE (?40; +80? C.)[ppm/K] Comparative example No. (Comp. Ex.) 13 14 15 16 Li.sub.2O 8.4 8.2 9.4 9.3 Na.sub.2O 0.05 0.35 0.1 0.25 K.sub.2O 0.6 0.25 MgO 1.8 ZnO 0.95 1.2 0.60 CaO 2.3 2.35 1.0 BaO 0.85 SrO Al.sub.2O.sub.3 16.55 16.5 17 18.95 SiO.sub.2 65.15 64.8 64.4 61.5 P.sub.2O.sub.5 3.4 3.3 3.5 4.05 TiO.sub.2 2.0 2.0 1.95 2.05 ZrO.sub.2 1.1 1.1 1.05 1.05 As.sub.2O.sub.3 0.15 0.2 0.2 0.15 Total 100.0 100.0 100.0 100.0 SiO.sub.2 + (5xLi.sub.2O) MgO + ZnO 0.95 1.2 1.8 0.60 ?R.sub.2O (R = Na, K, Cs, Rb) 0.05 0.35 0.7 0.50 ?RO (R = Ca, Ba, Sr) 2.25 2.35 1.85 Va [? C.] Ceram. temperature [? C.] 770 810 790 830 Ceram. time [days] 5 1 5 2.5 Cryst. phase [vol %] 73 69 74 66 Cryst. size [nm] 43 47 56 41 Av. CTE(0; +50? C.) [ppm/K] ?0.03 ?0.08 ?0.06 0.07 TCL (0; +50? C.) 4.29 |Expansion at 50? C.| 3.55 Index F 1.21 Hyst @ 45? C. [ppm] <0.1 <0.1 <0.1 <0.1 Hyst @ 35? C. [ppm] <0.1 <0.1 <0.1 <0.1 Hyst @ 30? C. [ppm] <0.1 <0.1 <0.1 <0.1 Hyst @ 22? C. [ppm] 0.13 <0.1 0.16 <0.1 Hyst @ 19? C. [ppm] 0.19 <0.1 <0.1 Hyst @ 15? C. [ppm] 0.28 0.16 0.11 Hyst @ 10? C. [ppm] 0.44 0.3 0.44 0.15 Hyst @ +5? C. [ppm] 0.67 0.55 0.63 0.23 Hyst @ 0? C. [ppm] 0.97 0.84 0.85 0.35 Ceram. temperature [? C.] Ceram. time [days] Av. CTE (?30; +70? C.)[ppm/K] Av. CTE (?40; +80? C.)[ppm/K]
TABLE-US-00008 TABLE 3 Alternative index f.sub.T.i. for selected Ex. and Comp. Ex. f.sub.T.i. Ti-dop. [ppm/K] SiO.sub.2 Ex. 2 Ex. 4 20-40? C. 0.024 0.020 0.019 20-70? C. 0.039 0.022 ?10-30? C. 0.015 0.005
[0185] While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.