OPTICAL GLASS WITH HIGH REFRACTIVE INDEX

Abstract

An optical glass has a refractive index n.sub.d of more than 2.10 and includes at least TiO.sub.2, NbO.sub.2.5, LaO.sub.1.5, SiO.sub.2, and B.sub.2O.sub.3. The glass has the following features: a cation parameter K of 1.8<K≤2.8, wherein K=(Ti-eq.+SiO.sub.2+(BO.sub.1.5)/2)/(La-eq.), the molar fractions of Ti-eq., SiO.sub.2, BO.sub.1.5 and La-eq. in the cation parameter K being in cat %; a sum total of glass components SiO.sub.2 and B.sub.2O.sub.3 of 8.0 mol %≤(SiO.sub.2+B.sub.2O.sub.3)≤20.0 mol %, the proportion of B.sub.2O.sub.3 being >0 mol % and the proportion of SiO.sub.2>0 mol %; and a temperature T.sub.max≤1330° C.

Claims

1. An optical glass having a refractive index n.sub.d of more than 2.10 and comprising at least TiO.sub.2, NbO.sub.2.5, LaO.sub.1.5, SiO.sub.2, and B.sub.2O.sub.3, the glass having the following features: a cation parameter K of 1.8<K≤2.8, wherein K=(Ti-eq.+SiO.sub.2+(BO.sub.1.5)/2)/(La-eq.), the molar fractions of Ti-eq., SiO.sub.2, BO.sub.1.5 and La-eq. in the cation parameter K being in cat %; a sum total of glass components SiO.sub.2 and B.sub.2O.sub.3 of 8.0 mol %≤(SiO.sub.2+B.sub.2O.sub.3)≤20.0 mol %, the proportion of B.sub.2O.sub.3 being >0 mol % and the proportion of SiO.sub.2>0 mol %; and a temperature T.sub.max≤1330° C.

2. The optical glass of claim 1, having an internal transmission τ.sub.i of at least 75% measured at a wavelength of 460 nm and a sample thickness of 10 mm.

3. The optical glass of claim 2, wherein the internal transmission is τ.sub.i at least 90%.

4. The optical glass of claim 1, having a density of <5.3 g/cm.sup.3 and/or a numerical value for a ratio (n.sub.d).sup.2/density of more than 0.85.

5. The optical glass of claim 1, wherein the proportion of the components TiO.sub.2 and LaO.sub.1.5 in the glass is at least 53.0 cat %.

6. The optical glass of claim 5, wherein the proportion of NbO.sub.2.5 is at least 7.0 cat %.

7. The optical glass of claim 1, wherein the proportion of the components TiO.sub.2, LaO.sub.1.5 and NbO.sub.2.5 is at least 60.0 cat %.

8. The optical glass of claim 1, having at least one of the following features: a proportion of Ti-eq. of at least 43.0 cat % and/or not more than 63.0 cat %; a proportion of La-eq. of at least 21.0 cat % and/or not more than 35.0 cat %; or a sum total (Ti-eq.+La-eq.) of at least 72.0 cat % and/or not more than 85.0 cat %.

9. The optical glass of claim 8, wherein the proportion of La-eq. is not more than 30.0 cat % and/or wherein the proportion of Ti-eq. is at least 45.0 cat %.

10. The optical glass of claim 1, wherein the cation parameter is at least 1.9.

11. The optical glass of claim 10, wherein the cation parameter is at least 2.2.

12. The optical glass of claim 1, comprising the following components in cat %: TABLE-US-00019 SiO.sub.2   >0 to <20.0; BO.sub.1.5   >0 to <20.0; TiO.sub.2 32.0 to 52.0; NbO.sub.2.5  3.0 to 15.0; ZrO.sub.2   0 to 11.0; WO.sub.3   0 to 5.0; TaO.sub.2.5   0 to 5.0; AlO.sub.1.5   0 to 5.0; SbO.sub.2.5   0 to 0.5; AsO.sub.2.5   0 to 0.5; LaO.sub.1.5 13.0 to 30.0; GdO.sub.1.5   0 to 10.0; YO.sub.1.5 0 to 5.0; and YbO.sub.1.5   0 to 5.0.

13. The optical glass of claim 1, comprising the following components in cat %: TABLE-US-00020 SiO.sub.2   >0 to <20.0; BO.sub.1.5   >0 to <20.0; TiO.sub.2 32.0 to 52.0; NbO.sub.2.5  4.0 to 15.0; ZrO.sub.2   0 to 11.0; WO.sub.3   0 to 5.0; TaO.sub.2.5   0 to 5.0; AlO.sub.1.5   0 to 5.0; SbO.sub.2.5   0 to 0.5; AsO.sub.2.5   0 to 0.5; LaO.sub.1.5 13.0 to 28.0; GdO.sub.1.5   0 to 10.0; YO.sub.1.5 0 to 5.0; and YbO.sub.1.5   0 to 5.0.

14. The optical glass of claim 1, comprising the following components in cat %: TABLE-US-00021 SiO.sub.2  2.0 to 14.0; BO.sub.1.5  1.0 to 18.0; TiO.sub.2 34.0 to 50.0; NbO.sub.2.5  5.0 to 13.0; ZrO.sub.2 2.0 to 8.0; WO.sub.3   0 to 2.0; TaO.sub.2.5   0 to 1.0; AlO.sub.1.5   0 to 2.0; SbO.sub.2.5   0 to 0.1; AsO.sub.2.5   0 to 0.1; LaO.sub.1.5 16.0 to 24.0; GdO.sub.1.5 2.0 to 8.0; YO.sub.1.5 0.3 to 2.0; and BaO   0 to 6.5.

15. The optical glass of claim 1, having a content of BaO of not more than 6.5 cat % and/or a content of TiO.sub.2 of at least 39 cat %.

16. The optical glass of claim 1, having an Abbe number (ν.sub.d) of more than 18.5 and/or less than 30.0.

17. The optical glass of claim 16, wherein the Abbe number is more than 18.9 and/or less than 25.0.

18. The optical glass of claim 1, wherein the glass, based on the respective cations, is essentially free of one or more constituents selected from group consisting of bismuth, lead, germanium, phosphate, lithium, magnesium, cadmium, gallium, coloring components, cobalt, vanadium, chromium, molybdenum, copper, nickel, and combinations thereof.

19. A glass article, comprising: an optical glass having a refractive index n.sub.d of more than 2.10 and comprising at least TiO.sub.2, NbO.sub.2.5, LaO.sub.1.5, SiO.sub.2, and B.sub.2O.sub.3, the glass having the following features: a cation parameter K of 1.8<K≤2.8, wherein K=(Ti-eq.+SiO.sub.2+(BO.sub.1.5)/2)/(La-eq.), the molar fractions of Ti-eq., SiO.sub.2, BO.sub.1.5 and La-eq. in the cation parameter K being in cat %; a sum total of glass components SiO.sub.2 and B.sub.2O.sub.3 of 8.0 mol %≤(SiO.sub.2+B.sub.2O.sub.3)≤20.0 mol %, the proportion of B.sub.2O.sub.3 being >0 mol % and the proportion of SiO.sub.2>0 mol %; and a temperature T.sub.max≤1330° C.; wherein the glass article is in the form of a glass substrate, a wafer, a lens, a spherical lens, a prism, an asphere, an optical waveguide, a fibre, and/or a plate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] 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 drawings, wherein:

[0015] FIG. 1 illustrates an internal transmission spectrum of exemplary glass 31 from Table 1;

[0016] FIG. 2 illustrates the relationship of the cation parameter K and Tmax for exemplary embodiments and comparative examples from Tables 1 to 9 and 14; and

[0017] FIG. 3 shows the relationship of the cation parameter K and Tmax for exemplary embodiments and comparative examples from the tables.

[0018] 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

[0019] In some embodiments, the invention relates to an optical glass having a refractive index n.sub.d of more than 2.10 that comprises at least TiO.sub.2, NbO.sub.2.5 and LaO.sub.1.5, the glass having the following features: [0020] a cation parameter K of 1.8<K≤2.8, where K=(Ti-eq.+SiO.sub.2+(BO.sub.1.5)/2)/(La-eq.), the molar fractions of Ti-eq., SiO.sub.2, BO.sub.1.5 and La-eq. in the cation parameter K being in cat %, [0021] a sum total of glass components SiO.sub.2 and B.sub.2O.sub.3 of 8.0 mol %≤(SiO.sub.2+B.sub.2O.sub.3)≤20.0 mol %, the proportion of B.sub.2O.sub.3 being >0 mol % and the proportion of SiO.sub.2>0 mol %. [0022] a temperature T.sub.max≤1330° C.

[0023] Exemplary embodiments provided according to the invention are based to a large extent on the correct setting of the molar fractions of cations of the glass components with respect to one another. It is therefore convenient to characterize the composition of the glass by specifying it in cat %. The glass does also contain anions, in particular oxygen. However, the properties of the glass provided according to the invention are determined less by the anions, consequently the core of the embodiments provided according to the invention lies more in the composition of the cations.

[0024] The term “cation-percent” (cat % for short) relates here to the relative molar fractions of the cations based on the total cation content of the glass. The glass does also contain anions, the relative molar fractions of which are described in anion-percent (an %) based on the total anion content of the glass. In the context of the invention, the cations are in each case specified in the highest oxidation state and shown charge-compensated with oxygen as anion. This does not mean that the cations are necessarily present in glass exclusively in the highest oxidation state. For example, in the case of arsenic and antimony, there may be cations in the trivalent oxidation state and in the pentavalent oxidation state present side-by-side in the glass. For better clarity, the element name of a composition, for example “niobium”, is also used in the description of the composition of the glass. This stands in this instance for “cations of niobium” and thus does not imply that niobium is present in elemental form in the glass.

[0025] In addition to the cations, the glass provided according to the invention also includes anions, which are optionally selected from the group consisting of O.sup.2−, F.sup.−, Br.sup.− and Cl.sup.−. The molar fraction of O.sup.2− can optionally be at least 50% (an %), at least 70%, at least 90%, or at last 99%, based on the anion content. In some embodiments, the glass contains only O.sup.2− as anion and is free of other anions.

[0026] Some compositional features are better described in terms of the molar fraction of the oxidic glass component. In such cases, the individual glass component or the sum total of the glass components is given in mol %. Values in mol % can be calculated from the glass composition specified in cat %.

[0027] In the context of the invention, a glass system comprising SiO.sub.2 that has a high TiO.sub.2 content has been found that—unlike the glasses produced from the niobium phosphate system or titanium phosphate system that are described in the background—are more stable in respect of the internal transmission that can be achieved and have a higher refractive index but yet a relatively low density. As the refractive index increases, so does the tendency to devitrification. An inventive glass has nevertheless been found that has n.sub.d>2.10 and is similarly stable in respect of devitrification to the known titanium-, niobium- and lanthanum-containing glasses.

[0028] An optical glass provided according to the invention has a defined ratio of the proportions (in cat %) of particular cations of the glass components, which is described as the cation parameter K and determined as follows:

K=(Ti-eq.+SiO.sub.2+(BO.sub.1.5)/2)/(La-eq.)

[0029] For the glasses provided according to the invention, the following applies: 1.8<K≤2.8.

[0030] This condition describes a composition range within which it is possible for the components that are advantageous for achievement of a high refractive index and high internal transmission to form an amorphous glass, i.e. without the formation of crystal phases. The challenge in such a high-refractive-index glass system is to obtain a stable glassy region alongside a low liquidus temperature. The condition according to the invention has allowed such a composition range to be found, which is described similarly to a miscibility gap in binary or ternary systems.

[0031] The glass here also has a temperature T.sub.max≤1330° C. and a n.sub.d of 2.10.

[0032] In the cation parameter K, cations of the glass composition are classified—as published for example in: R. D. Shannon; Revised Effective Ionic Radii and Systematic Studies of Interatomic Distances in Halides and Chalcogenides; Acta Crystallographica. Section A 32, 751, 1976—into various groups according to their crystal ion radii: [0033] titanium equivalent (Ti-eq.) is formed from the sum total of the molar fractions of the cations of titanium (TiO.sub.2), niobium (NbO.sub.2.5), zirconium (ZrO.sub.2), tungsten (WO.sub.3), tantalum (TaO.sub.2.5), aluminum (AlO.sub.1.5), antimony (SbO.sub.2.5) and arsenic (AsO.sub.2.5), i.e. ions having a relatively small ionic radius of <100 μm; [0034] lanthanum equivalent (La-eq.) is formed from the sum total of the molar fractions of the cations of lanthanum (LaO.sub.1.5), gadolinium (GdO.sub.1.5), yttrium (YO.sub.1.5) and ytterbium (YbO.sub.1.5), i.e. ions having a relatively large ionic radius of >100 pm. La-eq. is the divisor of the cation parameter.

[0035] Also included in the condition is the molar cat % of the glass formers (SiO.sub.2) and boron (BO.sub.1.5), which are added to the cat % proportion of the titanium equivalents and together with Ti-eq. form the dividend of the cation parameter. Since it is possible in a glass composition when considering the molar fractions to replace a SiO.sub.2 with a B.sub.2O.sub.3 with the refractive index remaining at about the same level, only half the cat % of BO.sub.1.5 is included in the condition, i.e. (BO.sub.1.5)/2.

[0036] By selecting and mixing cations of different size in a defined ratio in accordance with the invention, it is possible to effectively counteract crystal formation.

[0037] The cation parameter K is according to the invention greater than 1.8 and max. 2.8. If the cation parameter is 1.8 or less, then T.sub.max will be too high, with the result that internal transmission decreases through the ingress of refractory material and heightened reduction of polyvalent oxides brought about by the higher process temperatures that are necessary. In addition, the refractive index tends to fall when K is smaller, since lanthanum equivalents raise the refractive index less strongly than titanium equivalents. However, the cation parameter must not be too high either. A K value greater than 2.8 means that the glass contains too few lanthanum equivalents, which has an adverse effect on the tendency to crystallization and thus on T.sub.max. Moreover, if the glass has an excessively high cation parameter K and thus too many titanium equivalents, it will have a greater tendency to oxidation and thus to discoloration on account of the higher content of polyvalent oxides such as TiO.sub.2 and NbO.sub.2.5. An advantageous lower limit for the cation parameter may be at least or more than 1.9 or at least 2.0. Some exemplary embodiments have a lower limit for the cation parameter of more than 2.0 or a lower limit of at least or more than 2.1 or at least or more than 2.2 or at least or more than 2.25 or at least or more than 2.3. Some embodiments provided according to the invention may have an upper limit for the cation parameter K of at most or less than 2.75 or at most or less than 2.7 or, for some exemplary variants, of at most or less than 2.6.

[0038] In addition, in a glass provided according to the invention the sum total of the glass components SiO.sub.2 and B.sub.2O.sub.3 is at least 8.0 mol % and not more than 20.0 mol %, the proportion of B.sub.2O.sub.3 being >0 mol % and the proportion of SiO.sub.2>0 mol %. The proportions of the glass components SiO.sub.2 and B.sub.2O.sub.3 in mol % based on oxide can in each case be calculated from the composition stated in cat %. A glass provided according to the invention requires a sum total (SiO.sub.2+B.sub.2O.sub.3) of at least 8.0 mol %, optionally of more than 8.0 mol %, of at least 9.0 mol % or at least 10.0 mol %, in order for it to be possible for a glassy composition to form in the melting process. However, the sum total should not exceed an upper limit of 20.0 mol %, since otherwise the glass will contain too small a proportion of glass components that increase the refractive index and the resulting refractive index will thus be too low. An advantageous upper limit for the sum total SiO.sub.2+B.sub.2O.sub.3 may be <20 mol %. For some embodiments, the upper limit of the sum total SiO.sub.2+B.sub.2O.sub.3 may be max. 19.0 mol % or max. 18.0 mol %. Some embodiments may also have an upper limit for the sum total of max. 17.0 mol % or max. 16.5 mol %. B.sub.2O.sub.3 may optionally amount to at least 1.0 mol % or at least 1.5 mol % or at least 2.0 mol % and/or optionally not more than 19.0 mol % or not more than 17.0 mol % or not more than 15.0 mol % or not more than 13.0 mol % or not more than 12.0 mol %. SiO.sub.2 may optionally amount to at least 1.0 mol % or at least 2.0 mol % or at least 3.0 mol % and/or optionally not more than 19.0 mol % or not more than 18.0 mol % or not more than 16.0 mol % or not more than 15.0 mol %.

[0039] In addition, the glass provided according to the invention has a temperature T.sub.max of ≤1330° C. T.sub.max is a composition-dependent glass variable and indicates the temperature that is at least necessary in the melting process in order to generate a “blank” melt from the starting materials (for example raw materials, shards, etc.). A “blank” melt is present here when there are no remnants from melting—for example incompletely melted raw materials—and no crystals present in the melt. As explained in the introduction, the melting and refining temperatures should be as low as possible in order to avoid ingress of refractory material into the glass and coloration of the glass by polyvalent ions in a low oxidation state. This allows high internal transmission to be achieved. The requirement to achieve the highest-possible internal transmission means that the chosen melting and refining temperatures cannot be too high, consequently the melting temperature has an upper limit, hence the use also of the term “T.sub.max” for the temperature described here. T.sub.max is thus the lowest temperature at which a blank, crystal-free melt can still be produced. This relationship makes T.sub.max a good measure for the liquidus temperature of the glass (see below).

[0040] In the context of the invention, the T.sub.max of a glass composition is determined systematically on a laboratory scale in test series by melting the same glass from the starting components in small crucibles having a volume of in each case 20 ml at different maximum temperatures, with temperature increments of 10° C. chosen. Starting with the lowest temperature up to the highest temperature, the melting result is then visually evaluated in respect of whether a blank melt has been obtained or whether there are still remnants and/or crystals present in the glass.

[0041] The T.sub.max value determined for a composition in this way is reproducible even with laboratory melts of larger volume (e.g. 1 litre). Moreover, further experiments have shown that the temperature T.sub.max is only slightly above the liquidus temperature of the glass. It was inferred that the temperature T.sub.max, which can be determined in an easily operated laboratory procedure, is a good measure for the liquidus temperature of the glass, which is not determined exactly here.

[0042] In some embodiments, T.sub.max is less than 1330° C., for example not more than 1320° C., optionally not more than 1310° C., optionally not more than 1300° C. Some embodiments have a T.sub.max of not more than 1290° C. or not more than 1280° C.

[0043] In addition, a glass provided according to the invention has a refractive index n.sub.d of more than 2.10, which makes it possible for the system, for example a pair of AR eyeglasses, to achieve an advantageously greater FoV.

[0044] In some embodiments, the refractive index n.sub.d is more than 2.100, optionally at least 2.110, optionally at least 2.115, optionally at least 2.120, optionally at least 2.125 or optionally at least 2.130 or at least 2.133. An exemplary upper limit for n.sub.d may be 2.20 or 2.200 or 2.195 or 2.190 or 2.189. Overall, the refractive index can thus be within a range of from 2.10 to 2.20. The refractive index n.sub.d is known to those skilled in the art and refers in particular to the refractive index at a wavelength of about 587.6 nm (wavelength of the d line of helium). Those skilled in the art will know how the refractive index n.sub.d can be determined.

[0045] Optionally, the refractive index is determined with a refractometer, in particular with a V-block refractometer. In this case, samples having a square or approximately square base area (for example having dimensions of about 20 mm×20 mm×5 mm) may in particular be used. In the measurement with a V-block refractometer, the samples are generally placed in a V-shaped block prism having a known refractive index. The refraction of an incident light beam depends on the difference between the refractive index of the sample and the refractive index of the V-block prism, thereby allowing the refractive index of the sample to be determined. The measurement is optionally carried out at a temperature of 22° C.

[0046] In the context of the invention it has been possible to provide an optical glass having a refractive index n.sub.d of more than 2.10 and a low temperature T.sub.max, that is to say a low liquidus temperature, making it possible to provide a glass having high internal transmission.

[0047] An exemplary embodiment provided according to the invention has an internal transmission of at least 75%, at least 79%, at least 82% or at least 85% or at least 87% or at least 88% or at least 90% or at least 92% or at least 93% or at least 94% or at least 95% or at least 97%, measured at a wavelength of 460 nm and a sample thickness of 10 mm. When the glass is serving as a waveguide, the color impression is not distorted in the image that is generated in, for example, AR eyeglasses.

[0048] The internal transmission or degree of internal transmission can be measured using customary methods known to those skilled in the art, for example according to DIN 5036-1:1978. In this description, stated values for the internal transmission refer to a wavelength of 460 nm and a sample thickness of 10 mm. Stating a “sample thickness” does not mean that the glass has this thickness, but merely states the thickness to which the stated internal transmission refers.

[0049] Unless otherwise stated or obvious to those skilled in the art, measurements described herein are carried out at 20° C. and air pressure of 101.3 kPa.

[0050] In some embodiments provided according to the invention, the density of the glass is optionally <5.3 g/cm.sup.3, optionally <5.2 g/cm.sup.3 or <5.1 g/cm.sup.3 or <5.0 g/cm.sup.3.

[0051] In some embodiments provided according to the invention, the glasses have a low density in relation to a high refractive index, which allows weight savings to be made in optical components, for example in a pair of AR eyeglasses. This can be advantageous when the numerical value for the ratio (n.sub.d).sup.2/density is more than 0.85, optionally more than 0.87, optionally more than 0.89, optionally more than 0.90 and/or optionally more than 0.99, optionally less than 0.98, optionally less than 0.97.

[0052] In some embodiments provided according to the invention, the glass has an Abbe number, i.e. dispersion (ν.sub.d), of more than 18.5. Optionally, the dispersion is greater than 18.9, more optionally greater than 19.2 and/or more optionally greater than 19.5 and/or less than 30.0 or less than 25.0 or less than 24.0. ν.sub.d is calculated in known manner, by determining the refraction values n.sub.d (at about 587.6 nm), n.sub.F (at about 486 nm) and n.sub.C (at about 656 nm) using a refractometer and relating them to one another: v.sub.d=(n.sub.d−1)/(n.sub.F−n.sub.C).

[0053] In some embodiments, the glass has a glass transition temperature T.sub.g of 600° C. to 800° C. Optionally, T.sub.g may be more than 670° C., more than 700° C., optionally more than 720° C. A higher T.sub.g can be advantageous in respect of stability to crystallization since this means that the difference in temperature from T.sub.max is lower and the glass achieves a stable glassy state more rapidly. The glasses can however still readily undergo heat-forming and processing.

[0054] The average coefficient of thermal expansion (CTE) in the 20 to 300° C. temperature range should likewise not be too high, optionally in the range from 8.0 to 12.0 ppm/K, in the range from 8.3 to 11.5 ppm/K, optionally in the range from 8.5 to 11.0 ppm/K. The CTE is determined in accordance with DIN ISO 7991:1987.

[0055] The glass provided according to the invention contains titanium, niobium and lanthanum. Niobium-containing glasses are reputed to exhibit poorer internal transmission at the UV end of the visible range of the spectrum and, on account of the titanium content, to have a pronounced tendency to interfacial crystallization. These disadvantages to not occur with the lass described herein or occur only to a controllable degree.

[0056] Described below are the glass components that form the titanium equivalents (Ti-eq.) group:

[0057] The content of titanium (TiO.sub.2) in the glass may be at least 32.0 cat %, optionally at least 34.0 cat % or at least 35.0 cat %. In some embodiments the content is even at least 37.0 cat % or at least 38.0 cat %. Some embodiments may even contain at least 39 cat % of TiO.sub.2. The content of TiO.sub.2 may optionally be limited to not more than 52.0 cat %, not more than 50.0 cat %, not more than 49.0 cat % or not more than 48.0 cat % or not more than 47.0 cat %. In the glasses provided according to the invention, the component TiO.sub.2 takes on the role of glass formation and can therefore be described as an imperfect glass former. An excessively high TiO.sub.2 content would cause a sharp reduction in the Abbe number.

[0058] The proportion of niobium (NbO.sub.2.5) in the glass may be at least 3.0 cat %, optionally at least 4.0 cat %, optionally at least 4.5 cat %, optionally at least 5.0 cat % or at least 6.0 cat %. The content of NbO.sub.2.5 may optionally be limited to not more than 15.0 cat %, not more than 13.0 cat %, not more than 11.0 cat % or not more than 10.0 cat %. Some embodiments may even contain max. 9.0 cat %. Alongside TiO.sub.2 and LaO.sub.1.5, NbO.sub.2.5 contributes to a high refractive index. However, excessively high NbO.sub.2.5 contents are disadvantageous in this glass system and result in increased crystallization.

[0059] The proportion of zirconium (ZrO.sub.2) in the glass may be 0 to 11.0 cat %. There may be present in the glass at least 1.0 cat % or at least 2.0 cat %, optionally at least 3.0 cat % or at least 4.0 cat %, of ZrO.sub.2. ZrO.sub.2 can contribute to setting the cation parameter such that a glassy region with correspondingly low T.sub.max is achieved for the glass system. The content of ZrO.sub.2 may optionally be limited to not more than 11.0 cat %, not more than 10.0 cat %, not more than 9.0 cat % or not more than 8.0 cat %. Some embodiments may even contain max. 7.0 cat %. ZrO.sub.2 contributes to achieving the high refractive index, but at high amounts it also increases the tendency of the glass to crystallization, consequently its content is optionally limited. ZrO.sub.2-free variants are possible.

[0060] Tungsten (WO.sub.3) is an optional component of the glass. WO.sub.3 may be present in the glass in a content of max. 5.0 cat %, optionally max. 3.0 cat %, optionally max. 2 cat % or max. 1.5 cat % or max. 1 cat % or max. 0.7 cat %. When this component is present, a lower limit may be 0.1 cat %, optionally 0.3 cat %. WO.sub.3-free variants are possible and advantageous.

[0061] Tantalum (TaO.sub.2.5) is an optional component of the glass. TaO.sub.2.5 may be present in the glass in a content of max. 5.0 cat %, optionally max. 3.0 cat %, optionally max. 2.0 cat % or max. 1.0 cat % or max. 0.7 cat %. When this component is present, a lower limit may be 0.1 cat %, optionally 0.3 cat %. TaO.sub.2.5-free variants are also possible and may be advantageous.

[0062] Aluminum (AlO.sub.1.5) is an optional component of the glass that can contribute to the chemical resistance, but also to the refractive index of the glass. Its content may be from 0 to 5.0 cat % or up to 3.0 cat % or up to 2.0 cat % or up to 1.0 cat %. When AlO.sub.1.5 is present, it may be present in a proportion of at least 0.1 cat % or at least 0.5 cat %. Some embodiments are free of AlO.sub.1.5.

[0063] Antimony (SbO.sub.2.5) and arsenic (AsO.sub.2.5) are optional components and may be present in the glass in each case and independently of one another in a content of max. 0.5 cat %, optionally max. 0.3 cat % or max. 0.1 cat % or max. 0.05 cat %. When at least one of these components is present in the glass, 0.005 cat % may be a lower limit in each case. SbO.sub.2.5- and/or AsO.sub.2.5-free variants are possible. Since the melts of the glasses provided according to the invention have low thickness, the use of classical refining agents to reduce bubble formation can be dispensed with. Vacuum refining may optionally be employed. SbO.sub.2.5 and/or AsO.sub.2.5 may however be added to the mixture in order to keep the glass melt in an oxidizing state at high melting and refining temperatures so that polyvalent ions, especially titanium and niobium ions, are not present in their respective lower oxidation states, with the result that the internal transmission of the glass produced is improved.

[0064] It may be advantageous when the total proportion of titanium equivalents (Ti-eq.) in the glass, i.e. the sum total of TiO.sub.2+NbO.sub.2.5+ZrO.sub.2+WO.sub.3+AlO.sub.1.5+TaO.sub.2.5+AsO.sub.2.5+SbO.sub.2.5, is at least 43.0 cat % or at least 44.0 cat %. In some embodiments, the sum total may be at least 45.0 cat % or at least 46.0 cat %, optionally at least 47.0 cat %, optionally at least 49.0 cat % or at least 50.0 cat % and/or not more than 63.0 cat %, optionally not more than 61.0%, optionally not more than 59.0% or not more than 58.0%. An excessively high amount of titanium equivalent can result in crystallization and a high T.sub.max. The same applies to an excessively low amount.

[0065] In some embodiments provided according to the invention, the feature titanium equivalent is formed from the sum total of the molar fractions of the cations of titanium (TiO.sub.2), niobium (NbO.sub.2.5), zirconium (ZrO.sub.2), antimony (SbO.sub.2.5) and arsenic (AsO.sub.2.5), with the upper limits and/or lower limits stated above for the total proportion of titanium equivalents (Ti-eq.) accordingly applying. It is self-evident that the glasses in such embodiments are essentially free of WO.sub.3, AlO.sub.1.5 and TaO.sub.2.5.

[0066] In some embodiments, the feature titanium equivalent is formed from the sum total of the molar fractions of the cations of titanium (TiO.sub.2), niobium (NbO.sub.2.5) and zirconium (ZrO.sub.2), with the upper limits and/or lower limits stated above for the total proportion of titanium equivalents (Ti-eq.) accordingly applying. It is self-evident that the glasses in such embodiments are essentially free of WO.sub.3, AlO.sub.1.5, TaO.sub.2.5, AsO.sub.2.5 and SbO.sub.2.5.

[0067] In some embodiments, the following condition is satisfied: content of TiO.sub.2 (in cat %) >content of NbO.sub.2.5 (in cat %)>content of ZrO.sub.2 (in cat %).

[0068] Described below are the glass components forming the lanthanum equivalents (La-eq.) group:

[0069] The content of lanthanum (LaO.sub.1.5) in the glass may be at least 13.0 cat %, optionally at least 15.0 cat % or at least 16.0 cat %. In some embodiments the content is even at least 17.0 cat % or at least 18.0 cat %. In some embodiments the content is even at least 19.0 cat % or at least 20 cat %. The content of LaO.sub.1.5 may optionally be limited to not more than 30.0 cat % or not more than 29.0 cat %. Some embodiments may have a LaO.sub.1.5 content of not more than 28.0 cat %, not more than 26.0 cat %, not more than 25.0 cat % or not more than 24.0 cat % or not more than 23.0 cat %. Alongside TiO.sub.2 and NbO.sub.2.5, LaO.sub.1.5 contributes to a high refractive index. Excessively high contents of LaO.sub.1.5 contribute to increased devitrification and thus to an increase in T.sub.max.

[0070] The proportion of gadolinium (GdO.sub.1.5) in the glass may be 0 to 10.0 cat %. When it is present, the proportion may be at least 1.0 cat %, optionally at least 2.0 cat % or at least 3.0 cat %. The content of GdO.sub.1.5 may optionally be limited to not more than 10.0 cat %, not more than 9.0 cat %, not more than 8.0 cat % or not more than 7.0 cat %. Some embodiments may also contain max. 6.0 cat % or max. 5.0 cat % of GdO.sub.1.5.

[0071] Yttrium (YO.sub.1.5) is an optional component of the glass and may be present in the glass in a content of max. 5.0 cat %, optionally max. 3.0 cat %, optionally max. 2.0 cat % or max. 1.5 cat % or max. 1.0 cat %. When this component is present, a lower limit may be 0.1 cat %, optionally 0.3 cat %. YO.sub.1.5-free variants are possible.

[0072] Ytterbium (YbO.sub.1.5) is an optional component of the glass and may be present in the glass in a content of max. 5.0 cat %, optionally max. 3.0 cat %, optionally max. 2 cat % or max. 1.5 cat % or max. 1.0 cat %. When this component is present, a lower limit is advantageously 0.1 cat %, optionally 0.3 cat %. YO.sub.1.5-free variants are possible and may be advantageous.

[0073] It may be advantageous when the total proportion of lanthanum equivalents (La-eq.) in the glass, i.e. the sum total LaO.sub.1.5+GdO.sub.1.5+YO.sub.1.5+YbO.sub.1.5 in the glass is at least 21.0 cat %, optionally at least 22.0 cat %, optionally at least 23.0 cat % or at least 24.0 cat % and/or not more than 35.0 cat %, not more than 33.0 cat %, not more than 31.0 cat %. Some embodiments may also contain not more than 30.0 cat %, optionally not more than 29.0 cat %, optionally not more than 28.0 cat % or, in some embodiments, not more than 27.0 cat %, of lanthanum equivalents. An excessively high amount of lanthanum equivalent can result in crystallization and a high T.sub.max. The same applies to an excessively low amount.

[0074] In some embodiments, the feature lanthanum equivalent is formed from the sum total of the molar fractions of the cations of lanthanum (LaO.sub.1.5), gadolinium (GdO.sub.1.5) and yttrium (YO.sub.1.5), with the upper limits and/or lower limits stated above for the total proportion of lanthanum equivalents (La-eq.) accordingly applying. It is self-evident that the glasses in such embodiments are essentially free of YbO.sub.1.5.

[0075] In some embodiments, the following condition is satisfied: content of LaO.sub.1.5 (in cat %)>content of GdO.sub.1.5 (in cat %)>content of YO.sub.1.5 (in cat %).

[0076] In some embodiments, the proportion of the components TiO.sub.2 and LaO.sub.1.5 in the glass is at least 53.0 cat %, optionally at least 55.0 cat %, optionally at least 57.0 cat %, optionally at least 59.0 cat % and/or not more than 70.0 cat %, optionally not more than 69.0 cat % or not more than 68 cat %.

[0077] In some embodiments, the proportion of the components TiO.sub.2, LaO.sub.1.5 and NbO.sub.2.5 is at least 60.0 cat %, optionally at least 63.0 cat %, optionally at least 65.0 cat %, optionally at least 67.0 cat % and/or not more than 80.0 cat %, optionally not more than 77 cat % or not more than 75 cat %, optionally not more than 73.0 cat %.

[0078] For the optical glass it may be advantageous when the sum total (Ti-eq.+La-eq.) in the glass is at least 72.0 cat %, optionally at least 73.0 cat %, optionally at least 74.0 cat % and/or not more than 85.0 cat %, optionally not more than 84.0 cat %, optionally not more than 83.0 cat %. Some embodiments also have a lower limit for the sum total (Ti-eq.+La-eq.) of at least 75.0 cat % or at least 76.0 cat %. The higher the sum total, the higher the refractive index of the glass. However, as the sum total increases, so it also becomes more difficult to provide a glass that is stable to crystallization and has a high T.sub.max and accordingly high internal transmission.

[0079] Silicon (SiO.sub.2) is a glass former. The component contributes to the chemical resistance. If it is used in very large amounts, the refractive index values of the invention cannot be achieved. According to the invention, the glass contains SiO.sub.2 in a proportion of >0 cat %. Optionally, the glass contains at least 1.0 cat %, at least 2.0 cat % or at least 3.0 cat %. Some embodiments may also contain at least 4.0 cat % or at least 5.0 cat % of SiO.sub.2. The SiO.sub.2 content may be limited to less than 20.0 cat %, max. 18.0 cat % or max. 16.0 cat % or max. 14.0 cat % or max. 13.0 cat % or max. 12.0 cat %.

[0080] Boron (BO.sub.1.5) likewise acts as a glass former. In the glass system provided according to the invention it contributes to the lowering of temperature T.sub.max. According to the invention, the glass contains BO.sub.1.5 in a proportion of >0 cat %. Optionally, the glass contains at least 1.0 cat %, at least 2.0 cat % or at least 3.0 cat %. Some embodiments may also contain at least 4.0 cat % or at least 5.0 cat % or at least 6.0 cat % of BO.sub.1.5. The BO.sub.1.5 content may be limited to less than 20.0 cat %, max. 19.0 cat % or max. 18.0 cat %. Some embodiments contain BO.sub.1.5 in a proportion of max. 17.0 cat % or max. 16.0 cat % or max. 14.0 cat % or max. 12.0 cat % or max. 11.0 cat %.

[0081] With respect to the proportions of the components SiO.sub.2 and BO.sub.1.5, it should be noted that the proportions are to be selected such that the condition of 8.0 mol %≤(SiO.sub.2+B.sub.2O.sub.3)≤20.0 mol % is satisfied. Further exemplary upper limits and lower limits for this feature have already been stated hereinabove.

[0082] The glass may comprise barium (BaO). The content of BaO is in some embodiments restricted to not more than 6.5 cat %, not more than 6.0 cat %, in some embodiments to not more than 5.5 cat %, since excessively high proportions result in undesired crystallization. When BaO is present in the glass, this component may amount to at least 0.1 cat %, at least 0.2 cat %, at least 0.5 cat %, or at least 1.0 cat %, at least 2.0 cat % or at least 3.0 cat %. The presence of BaO in the glass can be helpful in ensuring the viscosity is higher and steeper in the high-viscosity range from approx. 10.sup.6 dPas to 10.sup.14 dPas. BaO-free variants are possible.

[0083] Zinc (ZnO), magnesium (MgO), calcium (CaO) and/or strontium (SrO) may optionally be used in the glass. They lower the melting temperature and stabilize the glass against crystallization without reducing its chemical resistance to the degree brought about by alkali metal oxides. The content of ZnO may here be from 0 to 5.0 cat %, up to max. 4.0 cat % or up to max. 3.0 cat % or up to max. 2.0 cat % or up to max. 1.0 cat %. Some embodiments are free of ZnO. The content of MgO may be from 0 to 2.0 cat % or up to max. 1.0 cat %. Some embodiments are free of MgO. The content of CaO may be from 0 to 2.0 cat % or up to max. 1.0 cat %. Some embodiments are free of CaO. The content of SrO may be from 0 to 2.0 cat % or up to max. 1.0 cat %. Some embodiments are free of SrO. For the components mentioned, an exemplary lower limit may in each case be at least 0.1 cat % or at least 0.3 cat % or at least 0.5 cat %.

[0084] Alkali metal oxides, such as LiO.sub.0.5, NaO.sub.0.5, KO.sub.0.5, RbO.sub.0.5, CsO.sub.0.5, may be present in the glass in a proportion for the individual components, in a proportion for the sum total thereof, of max. 2 cat %, max. 1 cat %, optionally max. 0.5 cat %. Small amounts of at least 0.1 cat % or at least 0.2 cat % (for the individual components or optionally for the sum total thereof) may be advantageous for the meltability of the glass. However, since these components lower the refractive index, there is an upper limit on the content thereof. Some embodiments are free of LiO.sub.0.5 and/or NaO.sub.0.5 and/or KO.sub.0.5 and/or RbO.sub.0.5 and/or CsO.sub.0.5, optionally free of alkali metal oxides.

[0085] Tin oxide (SnO.sub.2) shows only very low or no activity as a refining agent in the glass system provided according to the invention. It may however be present as a glass component in a proportion of max. 2 cat % or max. 1 cat % or max. 0.5 cat %. Optionally, the glass is SnO.sub.2-free.

[0086] Sulfate (SO.sub.3) may be present in a small proportion in the glass in order to stabilize higher oxidation states in polyvalent ions. When it is present, the proportion is at least 0.01 cat %. Higher proportions of sulfate increase the risk of pronounced bubble formation in the glass and the risk of platinum getting into the glass. The sulfate content may therefore be max. 0.5 cat %, optionally max. 0.1 cat %, optionally max. 0.05 cat %. Optionally, the glass is SO.sub.3-free.

[0087] The glass may contain small amounts of hafnium (HfO.sub.2), optionally max. 0.1 cat % or max. 0.05 cat %. It is generally not actively added but gets into the glass with the component ZrO.sub.2 via the raw material. If using very pure ZrO.sub.2 raw material, the glass may be HfO.sub.2-free.

[0088] The optical glass may comprise fluorine (F). Embodiments may contain max. 1 cat %, optionally max. 0.5 cat %, optionally max. 0.1 cat %, of this component. Some embodiments are free of F.

[0089] In some embodiments, the glass includes the following components in cat %:

TABLE-US-00001 SiO.sub.2   >0 to <20.0 BO.sub.1.5   >0 to <20.0 TiO.sub.2 32.0 to 52.0 NbO.sub.2.5  3.0 to 15.0 ZrO.sub.2   0 to 11.0 WO.sub.3   0 to 5.0 TaO.sub.2.5   0 to 5.0 AlO.sub.1.5   0 to 5.0 SbO.sub.2.5   0 to 0.5 AsO.sub.2.5   0 to 0.5 LaO.sub.1.5 13.0 to 30.0 GdO.sub.1.5   0 to 10.0 YO.sub.1.5   0 to 5.0 YbO.sub.1.5   0 to 5.0

[0090] In some embodiments, the glass includes the following components in cat %:

TABLE-US-00002 SiO.sub.2   >0 to <20.0 BO.sub.1.5   >0 to <20.0 TiO.sub.2 32.0 to 52.0 NbO.sub.2.5  4.0 to 15.0 ZrO.sub.2   0 to 11.0 WO.sub.3   0 to 5.0 TaO.sub.2.5   0 to 5.0 AlO.sub.1.5   0 to 5.0 SbO.sub.2.5   0 to 0.5 AsO.sub.2.5   0 to 0.5 LaO.sub.1.5 13.0 to 28.0 GdO.sub.1.5   0 to 10.0 YO.sub.1.5   0 to 5.0 YbO.sub.1.5   0 to 5.0

[0091] In some embodiments, the glass includes the following components in cat %:

TABLE-US-00003 SiO.sub.2  2.0 to 14.0 BO.sub.1.5  1.0 to 18.0 TiO.sub.2 34.0 to 50.0 NbO.sub.2.5  5.0 to 13.0 ZrO.sub.2 2.0 to 8.0 WO.sub.3   0 to 2.0 TaO.sub.2.5   0 to 1.0 AlO.sub.1.5   0 to 2.0 SbO.sub.2.5   0 to 0.1 AsO.sub.2.5   0 to 0.1 LaO.sub.1.5 16.0 to 24.0 GdO.sub.1.5 2.0 to 8.0 YO.sub.1.5 0.3 to 2.0 BaO   0 to 6.5

[0092] In some embodiments the glass consists to an extent of at least 95.0 cat %, of at least 98.0 cat % or of at least 99.0 cat %, of the components described herein, especially of the components listed in the tables above. In some embodiments the glass essentially consists entirely of these components.

[0093] As already explained above, the addition of classical refining agents is not necessary, since the melt has low thickness at the temperatures necessary for melting. When refining agents such as AsO.sub.2.5, SbO.sub.2.5, SO.sub.3 and/or Cl are nevertheless added, the content thereof can be significantly lowered, for example to <0.1 cat %. Pure physical refinement is moreover possible and may be advantageous. The glass may optionally include one or more of the following components having a refining effect in the stated proportions in cat %.

TABLE-US-00004 SbO.sub.2.5 0.0 to 0.5 AsO.sub.2.5 0.0 to 0.5 SO.sub.3 0.0 to 0.5 Cl 0.0 to 0.5

[0094] In some embodiments the glass is essentially free of cations of bismuth (BiG.sub.1.5) and/or lead (PbO). The addition of bismuth would increase the density of the glass disproportionately. Moreover, bismuth ions undergo reduction to elemental bismuth even at relatively low temperatures in the region of 1000° C., imparting a strong grey coloration to the glass. PbO is likewise avoided because of its adverse effect on a low density. It is also one of the toxic components.

[0095] The high contents of niobium, titanium and lanthanum means that costly components such as tantalum and/or tungsten and/or ytterbium and/or germanium (GeO.sub.2) are not necessary in the glass, or necessary only in small proportions, in order to obtain a glass having the desired high refractive index. Lithium is known for its aggressiveness towards ceramic bath and crucible materials and is therefore also where possible not used, or used only in small amounts.

[0096] Optionally, the glass is free of phosphate (PO.sub.2.5), since this makes the melt significantly reducing and thus significantly increases the oxygen requirement of the melt, which in turn increases platinum consumption, resulting in coloration of the glass.

[0097] Optionally, the glass is—based on the respective cations—essentially free of one or more constituents selected from magnesium, cadmium, gallium, germanium, coloring components—for example cobalt, vanadium, chromium, molybdenum, copper, nickel—and combinations thereof. Components such as iron, manganese, selenium, tellurium and/or thallium may be present in small proportions in the glass, for example they may get into the glass as impurities. Particularly iron, selenium and tellurium, but also manganese can act as redox partners. It may however be advantageous when these components too are not specifically added to the glass either individually or in combination

[0098] When this description states that the glass is free of a component or does not contain a certain component, what this means is that said component may at most be present as an impurity in the glass. This means that it is not added in significant amounts. Not significant amounts are amounts according to the invention of less than 100 ppm, optionally less than 50 ppm or less than 10 ppm (m/m).

[0099] In some embodiments, the invention relates to a glass article that includes or consists of the described glass. The glass article can take different forms. Optionally, the article has the form [0100] of a glass substrate, especially as a constituent of a stack of substrates for an optical component, especially in a pair of AR eyeglasses, [0101] a wafer, especially having a maximum diameter of 5.0 cm to 50.0 cm or having a diameter between 0.7 cm and 50 cm, optionally between 3 cm and 45 cm, or between 5 cm and 40 cm, [0102] a lens, especially a spherical lens, a prism or an asphere, and/or [0103] an optical waveguide, especially a fibre or plate.

[0104] In a further aspect the invention relates to the use of a glass or glass article described herein in AR eyeglasses, metaoptics, wafer-level optics, optical wafer applications or classical optics. Alternatively or in addition, the glass or glass article described herein may be used as a wafer, lens, spherical lens or optical waveguide.

[0105] The glasses provided according to the invention may be produced by melting commercial raw materials. For example, it is possible to melt the glasses in a device as described in the as yet unpublished DE 102020120168.

Examples

[0106] The compositions shown in Tables 1 to 14 that follow were melted and their properties investigated: Tables 1 to 13 show exemplary embodiments provided according to the invention (examples 1 to 99) and Table 14 comparative examples (comparative examples A to G). In some of the glasses the internal transmission was determined. The internal transmission of example 31 is shown in FIG. 1.

[0107] Compositions and Properties

TABLE-US-00005 TABLE 1 Cat % 1 2 3 4 5 6 7 8 AlO.sub.1.5 BO.sub.1.5 11.88 11.88 11.88 17.35 13.95 10.43 6.76 2.96 BaO 3.75 4.95 4.95 4.92 5.01 5.11 5.21 5.31 CaO GdO.sub.1.5 3.28 3.13 6.26 3.00 3.06 3.12 3.18 3.24 KO.sub.0.5 LaO.sub.1.5 22.97 21.92 18.79 21.02 21.42 21.82 22.24 22.68 NbO.sub.2.5 6.41 6.41 6.41 6.01 6.12 6.23 6.35 6.48 SiO.sub.2 4.75 4.75 4.75 3.65 5.58 7.58 9.66 11.82 SrO TiO.sub.2 42.70 42.70 42.70 40.04 40.78 41.55 42.36 43.19 YO.sub.1.5 ZnO ZrO.sub.2 4.27 4.27 4.27 4.00 4.08 4.16 4.24 4.32 WO.sub.3 TaO.sub.2.5 SbO.sub.2.5 AsO.sub.2.5 Cation 2.44 2.56 2.56 2.60 2.60 2.60 2.60 2.60 parameter B.sub.2O.sub.3 7.64 7.58 7.58 11.37 8.98 6.58 4.19 1.80 [mol %] SiO.sub.2 [mol %] 6.11 6.06 6.06 4.79 7.18 9.57 11.97 14.36 SiO.sub.2 + B.sub.2O.sub.3 13.75 13.64 13.64 16.16 16.16 16.15 16.16 16.16 [mol %] Properties T.sub.max [° C.] 1280 1280 1300 1300 1300 1300 1300 1320 n.sub.d 2.161 2.156 2.153 2.135 2.137 2.139 2.141 2.143 v.sub.d 20.4 20.5 20.3 20.8 20.8 20.8 20.8 20.9 Density 4.98 4.96 4.94 4.90 4.91 4.94 4.94 4.96 [g/cm.sup.3] n.sub.d.sup.2/Density 0.937 0.936 0.939 0.931 0.930 0.927 0.927 0.926

TABLE-US-00006 TABLE 2 Cat % 9 10 11 12 13 14 15 16 AlO.sub.1.5 0.61 BO.sub.1.5 10.43 10.43 10.43 10.43 10.43 10.43 10.43 10.43 BaO 4.95 5.16 5.16 4.64 4.64 5.16 5.16 5.16 CaO 0.52 GdO.sub.1.5 3.02 3.15 3.15 3.15 3.15 3.15 3.15 3.15 KO.sub.0.5 LaO.sub.1.5 21.13 22.03 22.03 22.03 22.03 21.02 22.03 22.03 NbO.sub.2.5 6.35 6.20 6.20 6.20 6.20 6.20 6.20 10.33 SiO.sub.2 7.58 7.58 6.98 7.58 7.58 7.58 7.58 7.58 SrO 0.52 TiO.sub.2 42.31 41.33 41.33 41.33 41.33 41.33 40.29 37.19 YO.sub.1.5 1.01 ZnO 1.03 ZrO.sub.2 4.23 4.13 4.13 4.13 4.13 4.13 4.13 4.13 WO.sub.3 TaO.sub.2.5 SbO.sub.2.5 AsO.sub.2.5 Cation 2.72 2.56 2.56 2.56 2.56 2.56 2.52 2.56 parameter B.sub.2O.sub.3 6.55 6.59 6.62 6.59 6.59 6.59 6.59 6.77 [mol %] SiO.sub.2 [mol %] 9.53 9.59 8.85 9.59 9.59 9.59 9.59 9.84 SiO.sub.2 + B.sub.2O.sub.3 16.08 16.18 15.47 16.18 16.18 16.18 16.18 16.61 [mol %] Properties T.sub.max [° C.] 1320 1280 1280 1280 1280 1280 1280 1280 n.sub.d 2.143 2.138 2.137 2.136 2.139 2.139 2.133 2.135 v.sub.d 20.6 20.9 20.9 20.9 20.8 20.9 21.1 21.1 Density 4.90 4.93 4.94 4.94 4.93 4.93 4.96 4.96 [g/cm.sup.3] n.sub.d.sup.2/Density 0.937 0.926 0.925 0.924 0.929 0.928 0.916 0.918

TABLE-US-00007 TABLE 3 Cat % 17 18 19 20 21 22 23 24 AlO.sub.1.5 BO.sub.1.5 10.43 10.43 6.76 10.43 10.43 10.43 9.52 9.52 BaO 5.16 5.16 5.26 5.19 5.16 5.19 5.31 5.23 CaO GdO.sub.1.5 3.15 3.15 3.21 3.17 3.15 3.17 3.24 3.19 KO.sub.0.5 LaO.sub.1.5 22.03 21.02 21.43 21.15 21.02 21.15 21.91 21.57 NbO.sub.2.5 6.20 6.20 6.32 6.18 6.20 6.18 6.42 6.48 SiO.sub.2 7.58 7.58 9.66 7.58 7.58 7.58 5.71 5.71 SrO TiO.sub.2 38.74 40.29 41.07 41.18 40.81 40.66 42.82 43.20 YO.sub.1.5 1.01 1.03 1.01 1.01 1.01 0.78 0.77 ZnO 1.03 1.05 0.52 0.51 ZrO.sub.2 6.72 4.13 4.21 4.12 4.13 4.12 4.28 4.32 WO.sub.3 TaO.sub.2.5 SbO.sub.2.5 AsO.sub.2.5 Cation 2.56 2.52 2.52 2.54 2.54 2.52 2.47 2.53 parameter B.sub.2O.sub.3 6.59 6.59 4.19 6.60 6.59 6.60 6.02 6.01 [mol %] SiO.sub.2 [mol %] 9.59 9.59 11.98 9.59 9.59 9.59 7.23 7.21 SiO.sub.2 + B.sub.2O.sub.3 16.18 16.18 16.17 16.19 16.18 16.19 13.25 13.22 [mol %] Properties T.sub.max [° C.] 1280 1300 1320 1300 1300 1300 1280 1290 n.sub.d 2.129 2.134 2.136 2.138 2.136 2.136 2.157 2.158 v.sub.d 21.5 21.1 21.1 20.9 21.0 21.0 20.6 20.5 Density 4.98 4.94 4.96 4.92 4.93 4.94 4.98 4.98 [g/cm.sup.3] n.sub.d.sup.2/Density 0.911 0.922 0.921 0.930 0.927 0.923 0.934 0.935

TABLE-US-00008 TABLE 4 Cat % 25 26 27 28 29 30 31 32 AlO.sub.1.5 BO.sub.1.5 9.52 9.52 7.41 7.41 7.41 7.41 10.43 10.43 BaO 5.15 5.07 5.37 5.29 5.21 5.12 5.16 5.19 CaO GdO.sub.1.5 3.14 3.09 3.28 3.23 3.18 3.13 3.15 3.17 KO.sub.0.5 LaO.sub.1.5 21.24 20.91 22.15 21.81 21.48 21.14 21.27 21.41 NbO.sub.2.5 6.54 6.59 6.78 6.84 6.90 6.96 6.20 6.18 SiO.sub.2 5.71 5.71 4.48 4.48 4.48 4.48 7.58 7.58 SrO TiO.sub.2 43.58 43.96 45.22 45.60 45.99 46.37 40.81 40.66 YO.sub.1.5 0.75 0.74 0.79 0.77 0.76 0.75 0.76 0.76 ZnO 0.52 0.51 ZrO.sub.2 4.36 4.40 4.52 4.56 4.60 4.64 4.13 4.12 WO.sub.3 TaO.sub.2.5 SbO.sub.2.5 AsO.sub.2.5 0.01 0.01 Cation 2.58 2.64 2.47 2.53 2.58 2.64 2.54 2.52 parameter B.sub.2O.sub.3 6.00 5.98 4.65 4.64 4.63 4.62 6.59 6.60 [mol %] SiO.sub.2 [mol %] 7.20 7.18 5.61 5.60 5.59 5.58 9.59 9.59 SiO.sub.2 + B.sub.2O.sub.3 13.20 13.16 10.26 10.24 10.22 10.20 16.18 16.19 [mol %] Properties T.sub.max [° C.] 1300 1290 1320 1310 1310 1290 1280 1280 n.sub.d 2.160 2.162 2.178 2.181 2.182 2.184 2.136 2.135 v.sub.d 20.4 20.3 20.1 20.0 19.9 19.8 21.0 21.0 Density 4.96 4.94 5.03 5.02 5.01 4.99 4.94 4.94 [g/cm.sup.3] n.sub.d.sup.2/Density 0.942 0.946 0.943 0.948 0.951 0.955 0.924 0.924

TABLE-US-00009 TABLE 5 Cat % 33 34 35 36 37 38 39 40 AlO.sub.1.5 BO.sub.1.5 10.43 10.43 10.43 10.43 10.43 10.43 10.43 9.52 BaO 5.11 5.16 5.16 4.64 4.64 4.64 5.16 5.18 CaO 0.52 GdO.sub.1.5 3.12 3.15 3.15 3.15 3.15 3.15 3.15 3.16 KO.sub.0.5 0.52 LaO.sub.1.5 21.07 21.27 21.27 21.27 21.27 21.27 21.27 21.37 NbO.sub.2.5 6.23 6.20 6.20 6.20 6.20 6.20 6.20 6.23 SiO.sub.2 7.58 7.58 7.58 7.58 7.58 7.58 7.58 8.10 SrO 0.52 TiO.sub.2 41.04 40.81 40.29 40.81 40.81 40.81 40.29 41.00 YO.sub.1.5 0.75 0.76 0.76 0.76 0.76 0.76 0.76 0.76 ZnO 0.52 0.52 0.52 0.52 0.52 0.52 0.52 0.52 ZrO.sub.2 4.16 4.13 4.13 4.13 4.13 4.13 4.13 4.15 WO.sub.3 0.52 TaO.sub.2.5 0.52 SbO.sub.2.5 AsO.sub.2.5 0.01 Cation 2.58 2.54 2.54 2.54 2.54 2.54 2.54 2.54 parameter B.sub.2O.sub.3 6.58 6.59 6.59 6.59 6.59 6.61 6.61 5.99 [mol %] SiO.sub.2 [mol %] 9.57 9.59 9.59 9.59 9.59 9.62 9.62 10.19 SiO.sub.2 + B.sub.2O.sub.3 16.15 16.18 16.18 16.18 16.18 16.23 16.23 16.18 [mol %] Properties T.sub.max [° C.] 1280 1300 1300 1300 1300 1300 1300 1300 n.sub.d 2.137 2.136 2.135 2.135 2.138 2.135 2.136 2.137 v.sub.d 20.9 21.0 20.9 21.0 20.9 21.0 21.0 21.0 Density 4.92 4.94 4.95 4.93 4.93 4.90 4.97 4.94 [g/cm.sup.3] n.sub.d.sup.2/Density 0.928 0.923 0.921 0.923 0.928 0.929 0.918 0.925

TABLE-US-00010 TABLE 6 Cat % 41 42 43 44 45 46 47 48 AlO.sub.1.5 BO.sub.1.5 11.32 11.32 11.32 7.69 9.52 10.43 8.61 8.61 BaO 5.13 5.26 5.18 5.28 5.18 4.64 5.27 5.19 CaO 0.52 GdO.sub.1.5 3.13 3.21 3.16 3.22 3.40 3.15 3.22 3.17 KO.sub.0.5 LaO.sub.1.5 21.17 21.70 21.37 21.78 22.98 21.27 21.75 21.41 NbO.sub.2.5 6.17 6.36 6.42 6.54 6.06 6.20 6.79 6.84 SiO.sub.2 7.08 4.72 4.72 6.73 7.62 7.58 3.83 3.83 SrO TiO.sub.2 40.62 42.42 42.79 43.62 39.88 39.78 44.68 45.06 YO.sub.1.5 0.75 0.77 0.76 0.77 0.82 0.76 0.77 0.76 ZnO 0.51 0.50 0.52 0.57 0.57 ZrO.sub.2 4.11 4.24 4.28 4.36 4.04 4.13 4.52 4.56 WO.sub.3 0.52 TaO.sub.2.5 0.52 SbO.sub.2.5 AsO.sub.2.5 0.01 Cation 2.54 2.47 2.53 2.53 2.29 2.54 2.49 2.55 parameter B.sub.2O.sub.3 7.19 7.23 7.21 4.81 6.06 6.61 5.42 5.41 [mol %] SiO.sub.2 [mol %] 8.99 6.02 6.01 8.41 9.69 9.62 4.82 4.81 SiO.sub.2 + B.sub.2O.sub.3 16.18 13.25 13.22 13.22 15.75 16.23 10.24 10.22 [mol %] Properties T.sub.max [° C.] 1300 1300 1310 1310 1320 1320 1320 1320 n.sub.d 2.136 2.156 2.157 2.160 2.134 2.136 2.177 2.178 v.sub.d 21.0 20.6 20.5 20.5 21.4 20.8 20.1 20.0 Density 4.93 4.97 4.96 4.98 5.00 4.92 5.03 5.02 [g/cm.sup.3] n.sub.d.sup.2/Density 0.925 0.934 0.938 0.937 0.912 0.927 0.941 0.945

TABLE-US-00011 TABLE 7 Cat % 49 50 51 52 53 54 55 56 AlO.sub.1.5 BO.sub.1.5 8.61 8.61 8.61 10.43 10.43 10.43 10.43 10.43 BaO 5.11 5.03 4.95 5.01 4.90 5.12 5.08 5.03 CaO GdO.sub.1.5 3.12 3.07 3.02 3.06 2.99 3.13 3.10 3.07 KO.sub.0.5 LaO.sub.1.5 21.07 20.74 20.40 20.67 20.21 21.14 20.94 20.74 NbO.sub.2.5 6.90 6.96 7.02 6.30 6.38 6.22 6.26 6.29 SiO.sub.2 3.83 3.83 3.83 7.58 7.58 7.58 7.58 7.58 SrO TiO.sub.2 45.43 45.81 46.19 41.48 42.01 40.96 41.18 41.41 YO.sub.1.5 0.75 0.74 0.72 0.73 0.72 0.75 0.74 0.74 ZnO 0.58 0.58 0.58 0.53 0.53 0.52 0.52 0.52 ZrO.sub.2 4.60 4.64 4.68 4.20 4.25 4.15 4.17 4.19 WO.sub.3 TaO.sub.2.5 SbO.sub.2.5 AsO.sub.2.5 Cation 2.61 2.67 2.73 2.65 2.74 2.56 2.60 2.64 parameter B.sub.2O.sub.3 5.40 5.39 5.38 6.57 6.55 6.59 6.58 6.57 [mol %] SiO.sub.2 [mol %] 4.80 4.79 4.78 9.55 9.52 9.58 9.57 9.55 SiO.sub.2 + B.sub.2O.sub.3 10.20 10.18 10.16 16.12 16.07 16.17 16.15 16.12 [mol %] Properties T.sub.max [° C.] 1320 1320 1320 1320 1320 1300 1300 1300 n.sub.d 2.180 2.182 2.184 2.139 2.142 2.137 2.138 2.139 v.sub.d 19.9 19.8 19.7 20.8 20.6 20.9 20.9 20.8 Density 5.01 5.00 4.98 4.91 4.89 4.93 4.92 4.91 [g/cm.sup.3] n.sub.d.sup.2/Density 0.949 0.953 0.957 0.932 0.938 0.927 0.929 0.931

TABLE-US-00012 TABLE 8 Cat % 57 58 59 60 61 62 63 64 AlO.sub.1.5 BO.sub.1.5 10.43 8.80 8.80 8.80 8.80 10.43 10.43 8.80 BaO 4.98 5.05 5.01 4.96 4.91 5.08 5.03 4.99 CaO GdO.sub.1.5 3.04 3.08 3.05 3.03 3.00 3.10 3.07 3.05 KO.sub.0.5 LaO.sub.1.5 20.54 20.85 20.65 20.45 20.25 20.94 20.74 20.58 NbO.sub.2.5 6.32 6.89 6.93 6.96 7.00 6.26 6.29 6.94 SiO.sub.2 7.58 4.02 4.02 4.02 4.02 7.58 7.58 4.02 SrO TiO.sub.2 41.63 45.39 45.62 45.84 46.07 41.18 41.41 45.69 YO.sub.1.5 0.73 0.74 0.73 0.73 0.72 0.74 0.74 0.73 ZnO 0.53 0.57 0.58 0.58 0.58 0.52 0.52 0.58 ZrO.sub.2 4.22 4.60 4.62 4.64 4.67 4.17 4.19 4.63 WO.sub.3 TaO.sub.2.5 SbO.sub.2.5 AsO.sub.2.5 0.01 0.01 Cation 2.67 2.65 2.68 2.72 2.76 2.60 2.64 2.70 parameter B.sub.2O.sub.3 6.56 5.51 5.50 5.50 5.49 6.58 6.57 5.50 [mol %] SiO.sub.2 [mol %] 9.54 5.03 5.02 5.02 5.01 9.57 9.55 5.02 SiO.sub.2 + B.sub.2O.sub.3 16.10 10.54 10.52 10.52 10.50 16.15 16.12 10.52 [mol %] Properties T.sub.max [° C.] 1300 1300 1300 1300 1300 1320 1320 1320 n.sub.d 2.140 2.179 2.180 2.181 2.182 2.139 2.139 2.180 v.sub.d 20.7 19.9 19.8 19.8 19.7 20.9 20.8 19.8 Density 4.91 4.99 4.99 4.98 4.97 4.92 4.91 4.99 [g/cm.sup.3] n.sub.d.sup.2/Density 0.934 0.950 0.953 0.955 0.957 0.930 0.931 0.953

TABLE-US-00013 TABLE 9 Cat % 65 66 67 68 69 70 71 AlO.sub.1.5 BO.sub.1.5 8.80 10.96 6.58 10.43 10.43 10.43 10.43 BaO 5.46 4.93 5.05 5.16 5.16 5.16 5.20 CaO GdO.sub.1.5 2.99 3.01 3.08 3.15 3.15 3.15 3.18 KO.sub.0.5 LaO.sub.1.5 20.19 20.35 20.82 21.27 21.27 21.27 21.47 NbO.sub.2.5 6.94 6.86 7.02 11.36 6.12 5.17 6.10 SiO.sub.2 4.02 2.84 5.22 7.58 8.25 7.58 8.15 SrO TiO.sub.2 45.69 45.17 46.22 35.64 40.29 40.81 40.64 YO.sub.1.5 0.72 0.72 0.74 0.76 0.76 0.76 0.76 ZnO 0.58 0.57 0.59 0.52 0.51 0.52 ZrO.sub.2 4.63 4.57 4.68 4.13 4.08 4.13 4.06 WO.sub.3 1.03 TaO.sub.2.5 SbO.sub.2.5 AsO.sub.2.5 0.01 0.01 0.01 Cation 2.75 2.70 2.70 2.54 2.54 2.54 2.53 parameter B.sub.2O.sub.3 5.48 6.94 4.07 6.81 6.59 6.55 6.60 [mol %] SiO.sub.2 [mol %] 5.01 3.59 6.46 9.91 10.42 9.52 10.31 SiO.sub.2 + B.sub.2O.sub.3 10.49 10.53 10.53 16.72 17.01 16.07 16.91 [mol %] Properties T.sub.max [° C.] 1300 1320 1300 1300 1300 1310 1300 n.sub.d 2.178 2.179 2.181 2.132 2.130 2.133 2.132 v.sub.d 19.8 19.8 19.8 21.3 21.1 20.8 21.4 Density 4.98 4.98 4.99 4.97 4.92 4.92 4.94 [g/cm.sup.3] n.sub.d.sup.2/Density 0.953 0.954 0.953 0.915 0.922 0.925 0.920

TABLE-US-00014 TABLE 10 Cat % 72 73 74 75 76 77 78 79 AlO.sub.1.5 BO.sub.1.5 12.38 12.38 12.38 12.38 16.18 12.21 12.03 11.85 BaO CaO GdO.sub.1.5 4.52 4.56 4.60 4.64 4.46 4.62 4.69 4.76 KO.sub.0.5 LaO.sub.1.5 25.69 25.93 26.16 26.39 25.40 26.26 26.67 27.09 NbO.sub.2.5 5.76 5.73 5.70 5.66 5.61 5.71 5.68 5.66 SiO.sub.2 8.44 8.44 8.44 8.44 6.25 8.36 8.27 8.18 SrO TiO.sub.2 37.94 37.72 37.50 37.28 36.96 36.66 36.47 36.29 YO.sub.1.5 0.93 0.94 0.95 0.96 0.92 0.95 0.97 0.98 ZnO 0.48 0.48 0.47 0.47 0.47 0.48 0.47 0.47 ZrO.sub.2 3.84 3.82 3.80 3.77 3.74 4.76 4.74 4.71 WO.sub.3 TaO.sub.2.5 SbO.sub.2.5 AsO.sub.2.5 Cation 2.00 1.97 1.94 1.92 1.97 1.93 1.89 1.85 parameter B.sub.2O.sub.3 8.22 8.23 8.24 8.26 10.97 8.12 8.02 7.92 [mol %] SiO.sub.2 11.20 11.22 11.24 11.26 8.48 11.12 11.03 10.94 [mol %] SiO.sub.2 + B.sub.2O.sub.3 19.42 19.45 19.48 19.52 19.45 19.24 19.05 18.86 [mol %] Properties T.sub.max [° C.] 1300 1300 1300 1300 1300 1300 1300 1300 n.sub.d 2.136 2.135 2.135 2.134 2.133 2.134 2.135 2.134 v.sub.d 21.6 21.6 21.7 21.8 21.6 21.9 21.8 21.6 Density 5.00 5.01 5.01 5.02 4.99 5.05 5.02 5.00 [g/cm.sup.3] n.sub.d.sup.2/Density 0.912 0.910 0.910 0.907 0.912 0.902 0.908 0.911

TABLE-US-00015 TABLE 11 Cat % 80 81 82 83 84 85 86 87 AlO.sub.1.5 BO.sub.1.5 11.68 11.85 11.94 12.21 11.68 11.85 12.03 10.52 BaO 1.66 1.63 1.60 1.57 3.11 3.06 3.01 5.15 CaO GdO.sub.1.5 4.58 4.50 4.42 4.33 4.06 3.99 3.92 3.92 KO.sub.0.5 LaO.sub.1.5 26.05 25.58 25.13 24.65 23.07 22.70 22.33 22.32 NbO.sub.2.5 4.54 4.57 4.60 4.62 4.73 4.75 4.78 4.81 SiO.sub.2 7.34 7.43 7.57 7.70 7.44 7.53 7.61 6.68 SrO TiO.sub.2 37.95 38.22 38.50 38.67 39.60 39.79 39.97 40.22 YO.sub.1.5 0.95 0.93 0.91 0.90 0.84 0.83 0.81 0.81 ZnO 0.48 0.48 0.48 0.49 0.50 0.50 0.50 0.51 ZrO.sub.2 4.77 4.81 4.84 4.86 4.98 5.00 5.03 5.06 WO.sub.3 TaO.sub.2.5 SbO.sub.2.5 AsO.sub.2.5 Cation 1.91 1.97 2.02 2.07 2.24 2.29 2.34 2.29 parameter B.sub.2O.sub.3 7.67 7.77 7.81 7.96 7.50 7.60 7.71 6.67 [mol %] SiO.sub.2 9.65 9.74 9.89 10.05 9.56 9.66 9.75 8.48 [mol %] SiO.sub.2 + B.sub.2O.sub.3 17.32 17.51 17.70 18.01 17.06 17.26 17.46 15.15 [mol %] Properties T.sub.max [° C.] 1320 1320 1300 1300 1300 1300 1300 1300 n.sub.d 2.134 2.134 2.134 2.134 2.134 2.134 2.134 2.134 v.sub.d 21.9 21.8 21.7 21.6 21.4 21.4 21.3 21.4 Density 5.07 5.04 5.03 5.00 4.98 4.96 4.94 5.00 [g/cm.sup.3] n.sub.d.sup.2/Density 0.898 0.904 0.905 0.911 0.914 0.918 0.922 0.911

TABLE-US-00016 TABLE 12 Cat % 88 89 90 91 92 93 94 95 AlO.sub.1.5 BO.sub.1.5 10.79 10.96 11.14 11.23 11.68 12.65 9.71 11.85 BaO 5.07 4.99 4.91 4.83 3.11 3.00 5.02 4.82 CaO GdO.sub.1.5 3.86 3.80 3.74 3.68 4.06 3.91 3.82 3.67 KO.sub.0.5 LaO.sub.1.5 21.96 21.62 21.27 20.93 23.07 22.26 21.76 20.86 NbO.sub.2.5 4.82 4.84 4.86 4.89 4.73 4.77 4.86 4.87 SiO.sub.2 6.81 6.90 6.99 7.13 7.44 7.17 7.71 6.77 SrO TiO.sub.2 40.31 40.50 40.69 40.89 39.60 39.92 40.70 40.76 YO.sub.1.5 0.80 0.79 0.77 0.76 0.84 0.81 0.79 0.76 ZnO 0.51 0.51 0.51 0.51 0.50 0.50 0.51 0.51 ZrO.sub.2 5.07 5.09 5.12 5.14 4.98 5.02 5.12 5.13 WO.sub.3 TaO.sub.2.5 SbO.sub.2.5 AsO.sub.2.5 0.01 0.01 0.01 0.01 Cation 2.34 2.40 2.45 2.51 2.24 2.34 2.40 2.51 parameter B.sub.2O.sub.3 6.84 6.94 7.04 7.09 7.50 8.13 6.10 7.50 [mol %] SiO.sub.2 8.63 8.73 8.83 8.99 9.56 9.21 9.69 8.57 [mol %] SiO.sub.2 + B.sub.2O.sub.3 15.47 15.67 15.87 16.08 17.06 17.34 15.79 16.07 [mol %] Properties T.sub.max [° C.] 1300 1300 1300 1300 1300 1300 1300 1300 n.sub.d 2.134 2.134 2.134 2.134 2.133 2.134 2.134 2.134 v.sub.d 21.4 21.3 21.2 21.1 21.4 21.2 21.3 21.1 Density 4.98 4.97 4.95 4.94 4.98 4.94 4.97 4.93 [g/cm.sup.3] n.sub.d.sup.2/Density 0.914 0.916 0.920 0.922 0.914 0.922 0.916 0.924

TABLE-US-00017 TABLE 13 Cat % 96 97 98 99 AlO.sub.1.5 BO.sub.1.5 12.73 12.38 12.21 11.83 BaO 4.77 CaO GdO.sub.1.5 4.47 4.52 4.44 3.63 KO.sub.0.5 LaO.sub.1.5 25.41 25.69 25.25 20.78 NbO.sub.2.5 5.74 5.76 5.79 4.82 SiO.sub.2 8.61 8.44 8.92 6.37 SrO TiO.sub.2 37.80 37.94 38.13 41.60 YO.sub.1.5 0.92 0.93 0.92 0.77 ZnO 0.48 0.48 0.48 0.53 ZrO.sub.2 3.83 3.84 3.86 4.89 WO.sub.3 TaO.sub.2.5 SbO.sub.2.5 AsO.sub.2.5 0.008 Cation 2.02 2.00 2.05 2.12 parameter B.sub.2O.sub.3 8.45 8.22 8.06 7.49 [mol %] SiO.sub.2 11.43 11.20 11.78 8.07 [mol %] SiO.sub.2 + B.sub.2O.sub.3 19.88 19.42 19.84 15.56 [mol %] Properties T.sub.max [°C] 1320 1300 1320 1280 n.sub.d 2.134 2.136 2.135 2.134 ν.sub.d 21.6 21.6 21.5 21.3 Density 4.98 5.00 4.97 4.95 [g/cm.sup.3] n.sub.d.sup.2/Density 0.914 0.912 0.917 0.920

TABLE-US-00018 TABLE 14 Cat % A B C D E F G AlO.sub.1.5 BO.sub.1.5 6.57 11.88 7.69 10.43 BaO 10.71 14.82 8.44 3.84 4.54 10.34 5.04 CaO GdO.sub.1.5 4.00 2.87 2.57 3.08 KO.sub.0.5 LaO.sub.1.5 15.29 21.18 22.56 19.62 20.09 17.14 20.81 NbO.sub.2.5 5.54 4.64 5.09 9.61 6.71 6.62 21.98 SiO.sub.2 12.50 12.50 12.50 13.42 4.75 6.25 7.58 SrO TiO.sub.2 52.28 43.78 48.03 38.13 44.70 44.15 25.64 YO.sub.1.5 0.82 0.74 ZnO 0.52 ZrO.sub.2 3.69 3.09 3.39 4.81 4.47 4.42 4.19 WO.sub.3 TaO.sub.2.5 SbO.sub.2.5 AsO.sub.2.5 Cation 4.84 3.02 3.06 2.93 2.90 3.18 2.62 parameter B.sub.2O.sub.3 4.10 7.49 4.66 7.29 [mol %] SiO.sub.2 [mol %] 13.95 14.35 14.51 16.75 6.00 7.57 10.61 SiO.sub.2 + B.sub.2O.sub.3 13.95 14.35 14.51 20.85 13.49 12.23 17.90 [mol %] Properties T.sub.max [° C.] 1370 1450 1350 1390 1380 1360 1350 n.sub.d 2.154 2.107 2.149 2.121 2.166 2.142 2.125 v.sub.d 19.3 21.6 20.4 21.0 19.8 20.4 21.7 Density 4.70 4.95 4.91 4.84 4.90 4.90 5.03 [g/cm.sup.3] n.sub.d.sup.2/Density 0.987 0.897 0.940 0.930 0.958 0.937 0.897

FIGURES

[0108] FIG. 1 shows an internal transmission spectrum of exemplary glass 31 from Table 1. It can be seen that this example exhibits at 460 nm an internal transmission T.sub.i of more than 88% at a sample thickness of 10 mm. In addition, the transmission curve shows the advantageously steep fall from the visible region of the spectrum to the adjoining UV region.

[0109] FIG. 2 shows the relationship of the cation parameter K and T.sub.max for exemplary embodiments and comparative examples from Tables 1 to 9 and 14. It can be seen that the glasses provided according to the invention from Tables 1 to 9 have a cation parameter in the range from above 2.0 and max. 2.8 and at the same time a T.sub.max of in this case less than 1330° C., i.e. they have a relatively low liquidus temperature. In addition, all examples have a refractive index n.sub.d of more than 2.10. Thus, what has been found in the context of the invention is a stable glassy range alongside a low liquidus temperature in a high-refractive-index glass system.

[0110] FIG. 3 shows the relationship of the cation parameter K and T.sub.max for exemplary embodiments and comparative examples from the tables. In addition to the exemplary embodiments shown in FIG. 2, the exemplary embodiments of Tables 10 to 12 are depicted. It can be seen that even examples having a cation parameter in the range from above 1.8 to 2.0 alongside a refractive index of more than 2.10 may at the same time have a T.sub.max here of less than 1330° C., i.e. they may have a relatively low liquidus temperature.

[0111] In the context of the invention, it was found that glasses having a cation parameter of more than 2.0 have a lower tendency to crystallization than glasses having a cation parameter of max. 2.0, which have a stronger tendency to crystallization. A higher tendency to crystallization narrows the process window during production, making production more laborious for such glasses. In the process window the temperature of the melt is above T.sub.max. However, in order that the viscosity is not too low and for it to still be possible for the glass to be handled, for example with regard to hot forming, the chosen temperature cannot be too high. A further consequence of an increased tendency to crystallization may be, for example, that it is possible to produce only smaller glass articles.

[0112] 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.