Strongly scattering ceramic converter and method for producing same

Abstract

A strongly scattering optoceramic converter material having a density of less than 97% is provided, as well as a method for producing such an optoceramic material. By appropriately choosing in particular the composition, blending method, and sintering conditions, the production method permits to produce converter materials with tailored properties.

Claims

1. A single-phase porous optoceramic, comprising: a ceramic phase A.sub.3B.sub.5O.sub.12, wherein A is selected from a group consisting of Y, Gd, Lu, and combinations thereof, wherein B is selected from a group consisting of Al, Ga, and combinations thereof, and wherein the ceramic phase A.sub.3B.sub.5O.sub.12 comprises Ce as at least one active element; a density, based on a theoretical density, of between 90 and 96.5% with pores having a polygonal shape; and particles not integrated into the ceramic phase A.sub.3B.sub.5O.sub.12 that are in a range from 0 vol % to less than 5 vol %, wherein the optoceramic is configured to at least partially convert excitation light having a first wavelength into emitted light having a second wavelength, wherein the emitted light is emitted from a side of the optoceramic on which the excitation light is incident, wherein the optoceramic is configured to remit and combine at least a portion of the excitation light with the emitted light, wherein the optoceramic exhibits, when measured at a sample thickness of 1 mm, a remission at 600 nm that is from 0.75 to 0.95, wherein the optoceramic is configured for operation in remission, and wherein the optoceramic exhibits a quantum efficiency that is greater than 85%.

2. The optoceramic of claim 1, wherein the particles not integrated into the ceramic phase A.sub.3B.sub.5O.sub.12 are less than 1.5 vol %.

3. The optoceramic of claim 1, wherein the pores have a mean pore size from 0.1 to 100 micrometers.

4. The optoceramic of claim 1, wherein the ceramic phase A.sub.3B.sub.5O.sub.12 mainly comprises Y.sub.3Al.sub.5O.sub.12.

5. The optoceramic of claim 1, wherein the ceramic phase A.sub.3B.sub.5O.sub.12 mainly comprises Lu.sub.3Al.sub.5O.sub.12.

6. The optoceramic of claim 1, wherein the ceramic phase A.sub.3B.sub.5O.sub.12 comprises yttrium and/or lutetium as a first element A and gadolinium as a second element A.

7. The optoceramic of claim 6, wherein the gadolinium comprises Gd.sub.2O.sub.3 and has a content with respect to the A site that is from 0.5 to 8 mol %.

8. The optoceramic of claim 1, wherein A comprises Gd.sub.2O.sub.3 in a content with respect to the A site that is from 0.5 to 8 mol %.

9. The optoceramic of claim 1, wherein the ceramic phase A.sub.3B.sub.5O.sub.12 comprises aluminum as a first element B and gallium as a second element B.

10. The optoceramic of claim 9, wherein the gallium comprises Ga.sub.2O.sub.3 and has a content with respect to the B site that is from 0.5 to 15 mol %.

11. The optoceramic of claim 1, wherein B comprises Ga.sub.2O.sub.3 in a content with respect to the A site that is from 0.5 to 15 mol %.

12. The optoceramic of claim 1, wherein the Ce has a content from 0.001 to 3 wt %.

13. The optoceramic of claim 1, wherein the Ce has a content from 0.01 to 3 wt %.

14. The optoceramic of claim 1, further comprising a further active element selected from the group consisting of Pr, Sm, and Tb.

15. The optoceramic of claim 1, further comprising a thickness from 150 to 250 micrometers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the measurement setup for measuring remission at 600 nm for evaluation of scattering;

(2) FIG. 2 illustrates the relationship between remission at 600 nm and density;

(3) FIG. 3 illustrates the influence of the blending method and the sintering temperature on the density of the optoceramic;

(4) FIG. 4 illustrates the influence of the blending method and the sintering temperature on the remission at 600 nm of an optoceramic of 1 mm thickness;

(5) FIG. 5 illustrates the influence of the blending method and the sintering temperature on the remission of the blue excitation light;

(6) FIG. 6 illustrates the influence of the blending method and the sintering temperature on the quantum efficiency of the converter;

(7) FIG. 7 illustrates the influence of the blending method and the sintering temperature on the color location of the light emitted from the excited converter;

(8) FIG. 8 shows the color location of the converter material as a function of the material system, Ce content, and gadolinium content;

(9) FIG. 9 is an SEM image of a ceramic according to the invention;

(10) FIG. 10 is an SEM image of the ceramic shown in FIG. 9, with 10× magnification;

(11) FIG. 11 illustrates the influence of the blending method on the homogeneity of the ceramic converter;

(12) FIG. 12 shows the emission spectrum of a converter for generating white light operated in remission.

DETAILED DESCRIPTION

(13) FIG. 1 shows the measurement setup for measuring remission at 600 nm for evaluating scattering.

(14) The measurement was performed in a spectrophotometer with integrating sphere, for example in a Lambda 950 from manufacturer Perkin Elmer. Light from a grating monochromator 101 is incident on the sample 102 to be measured. The sample is slightly tilted, which means it is measured including the Fresnel reflection. The sample has a thickness of 1 mm. This value has been chosen arbitrarily, but must always be the same, for comparability of the measurements. The light remitted from the sample is measured by means of the integrating sphere 103. By referring to a previously measured remission standard, the absolute remission of the sample can be measured. For a passive scatterer of a given thickness d, remission is a monotonically increasing function of scattering length S and is therefore an appropriate measure for the scattering behavior of the ceramic converter.

(15) FIG. 2 shows the relationship between the density of a sintered optoceramic and its remission at 600 nm.

(16) The density was determined by geometrical measurement and weighing of the sintered samples. Typical sample geometries are cylinders having a diameter of 15 mm and a height of about 10 mm, but the density may be determined on samples of other geometries and sizes as well. The density values are based on the theoretical density.

(17) FIG. 2 shows that a low density generally results in high remission. In particular at densities of greater than 97%, remission drops steeply. The range 1 according to the invention, by contrast, is distinguished by high remission. Furthermore, FIG. 2 shows that ceramics having the same or very similar densities may exhibit different remission values. This illustrates that the remission of optoceramics according to the invention may be influenced not only by the density, but by further parameters such as the composition and activator content.

(18) FIG. 3 illustrates that in addition to the selected sintering temperature the density of the optoceramic depends on the blending method.

(19) Important production parameters of the converters illustrated in FIG. 3 are summarized in Table 1.

(20) TABLE-US-00001 TABLE 1 Maximum Sintering Material Ce.sub.2O.sub.3 Temperature Sample Application System [wt %] [° C.] Blender 2a white light YAG 0.1 1650 roller bench/ tumbler 2b white light YAG 0.1 1680 roller bench/ tumbler 2c white light YAG 0.1 1700 roller bench/ tumbler 3a white light YAG 0.1 1650 roller bench/ roller bench 3b white light YAG 0.1 1680 roller bench/ roller bench 3c white light YAG 0.1 1700 roller bench/ roller bench 3d white light YAG 0.1 1750 roller bench/ roller bench

(21) All measurements were performed on converters of 1 mm thickness in order to guarantee comparability and to ensure that the blue excitation light is completely absorbed in a single passage of the light. By contrast, in applications converters of 200 μm thickness are typically employed, optionally in combination with rear side reflectors.

(22) The optoceramics of the illustrated regime 2 were prepared using an embodiment of the method according to the invention in which in step c) the suspension including the starting materials and grinding media were homogenized in the first homogenization step using a roller bench, i.e. by a single axis movement. The second homogenization step, however, was performed using a tumbler, i.e. by a two axes movement. By contrast, the optoceramics of regime 3 were blended using a roller bench in both the first and the second homogenization steps.

(23) FIG. 3 clearly shows the influence of the blending method on the density of the resulting optoceramic. The ceramics of regime 2 have a high density already at low temperatures. The optoceramics of regime 3, on the other hand, have much lower densities with the same sintering temperature. Surprisingly, FIG. 3 shows that the blending method may have a greater influence on the density than the sintering temperature. For example, a sample for which the second homogenization step was performed using a tumbler exhibits a similar density with a sintering temperature of 1650° C. as a sample for which a roller bench was used in both homogenization steps and sintering was performed at a significantly higher sintering temperature of 1750° C.

(24) FIG. 4 shows the relationship between remission at 600 nm and the employed sintering temperature as well as the dependence thereof on the blending method applied. Regimes 2 and 3 are identical to the regimes described with reference to FIG. 3. Here, too, the great influence of the blending method on the remission of the optoceramic is apparent and the significance of the blending method for the optical properties of the optoceramic is demonstrated.

(25) FIG. 5 illustrates the influence of the blending method and the sintering temperature on the remission of the blue excitation light.

(26) The remission of blue excitation light is much lower than the remission at 600 nm shown in FIG. 4, since a portion of the blue excitation light is absorbed. Therefore, since the remission of blue excitation light depends on the concentration of the active element, this quantity is not suitable for an absolute evaluation of scattering, however it substantially determines the color location of the light emitted from the converter. For the measurement method selected here, the lower limit for remission is defined by the Fresnel reflection of the converter.

(27) FIG. 6 shows the influence of the blending method and the sintering temperature on the quantum efficiency of the converter.

(28) In the converters according to the invention, surprisingly, the quantum efficiency is substantially independent of the sintering temperature and the blending method. This permits to obtain highly scattering and yet efficient converters.

(29) FIG. 7 shows the influence of the blending method and the sintering temperature on the color location of the light emitted from the excited converter.

(30) The color locations of the CIE 1931 color space achievable for a specific converter substantially lie on a line that extends between the color location of the blue excitation light and the color location of the converted light. The position on this line is defined by the mixing ratio of blue and converted light and may therefore be adjusted in the converter of the invention by selecting the sintering temperature and the blending method. The color location was measured using quantum efficiency measuring system Hamamatsu C9920.

(31) FIG. 8 shows the influence of the sintering temperature and the composition of the optoceramic on the color location. The color location was measured using quantum efficiency measuring system Hamamatsu C9920.

(32) Material system, sintering temperature, gadolinium addition, and further production parameters of samples 2a to 7 of FIG. 8 are listed in Table 2:

(33) TABLE-US-00002 TABLE 2 Gd Maximum instead Sintering Material Ce.sub.2O.sub.3 of Y Temperature Sample Application System [wt %] [%] [° C.] Blender  2a white light YAG 0.1 0 1650 roller bench/tumbler  3b white light YAG 0.1 0 1680 roller bench/roller bench 4 white light - YAG:Gd 0.1 5 1630 roller bench/tumbler warm 5 white light - YAG:Gd 0.1 10 1630 roller bench/tumbler warm 6 saturated YAG 0.2 0 1700 roller bench/tumbler color - yellow 7 saturated LuAG 0.1 0 1700 roller bench/roller color - bench green

(34) FIG. 8 illustrates that the color location may be adjusted not only via the material system (LuAG, YAG), but also via the sintering temperature as well as via a variation of the composition (addition of gadolinium in this case).

(35) FIG. 9 shows an SEM image of a sample according to the invention. For taking the SEM image, a breaking edge of the sample was placed in a sample holder and then coated with carbon by vapor deposition. The breaking surface was observed under a scanning electron microscope. Pores 11 are uniformly distributed across the measured surface of the ceramic. The pores have a homogenous size distribution.

(36) FIG. 10 shows the SEM image of the sample illustrated in FIG. 9 with 10× magnification. The polygonal shape of pores 11 is clearly visible.

(37) FIG. 11 shows the influence of the blending method on the homogeneity of the ceramic converter. The photograph shows two converter plates, each one with a thickness of 200 μm and with a diameter of 15 mm. The material composition of the converters is identical, and both of them were sintered in the same sintering process. Only the blending method was different. As can be seen, the sample for which the second homogenization step was performed using a tumbler exhibits a significantly better homogeneity.

(38) FIG. 12 shows the emission spectrum of a converter operated in remission and intended for generating white light.

(39) This spectrum was not acquired using the quantum efficiency measurement system, but from a light source of a configuration comprising a converter of 200 μm thickness bonded to a highly reflective metallic mirror and with the blue excitation light incident on the converter at an angle of 60°. Excitation was effected with an optical power of up to 3 W on a light spot of less than 600 m diameter.

(40) The spectrum was measured using an integrating sphere located at a distance of 15 cm in the direction of the surface normal of the converter. Therefore, the Fresnel reflection of the excitation light does not contribute to the measured useful light here. The color coordinates of the light source for the 2° observer in the CIE 1931 coordinate system are (cx/cy)=(0.316/0.340). In order to obtain this color impression close to the white point, the power portion of the blue light has to be about 27%. This is made possible by a strongly scattering converter which diffusely remits about 20% of the blue excitation light. The good mechanical properties of the converter material have been proven by the preparation of the converter with 200 μm thickness. The good thermal properties of the converter material have been proven by the exposition of the converter to high power densities without causing damage.

(41) The preparation of the following groups of materials will now be explained in more detail below.

(42) Example for Producing a Translucent Y.sub.3Al.sub.5O.sub.12 Ceramic Including CeO.sub.2 by Uniaxial Compressing (with Reactive Sintering):

(43) Powders comprising primary particles having diameters of less than 1 μm, preferably diameters <300 nm, of Al.sub.2O.sub.3, Y.sub.2O.sub.3, and CeO.sub.2 are weighed in proportions according to the target composition. The target composition may vary around the stoichiometric range of the garnet composition, i.e. may in particular extend by 0.01 to 2.5 mol % to the Y.sub.2O.sub.3-rich side or by 0.01 to 2.5 mol % to the Al.sub.2O.sub.3-rich side. The CeO.sub.2 is stoichiometrically calculated to the Y site and ranges between 0.01 and 3 wt %. After addition of 0.5 to 3 wt % of dispersing and/or binding agents, the mixture is blended in a ball mill using ethanol and Al.sub.2O.sub.3 balls, for 12 to 16 hours. After the mixture was allowed to stand in the milling container for 5 to 12 hours, a second homogenization may be performed in a tumbling blender for 12 to 20 hours. Optionally, TEOS may be added to the mixture before the second blending operation as a sintering aid, so that the equivalent of between 0 and 0.5 wt % of SiO.sub.2 is used.

(44) The milled suspension is selectively dried on a rotary evaporator or granulated in a spray dryer.

(45) The powder is then uniaxially compressed into plates or bars. Uniaxial pressure conditions are between 10 and 50 MPa, pressure durations between a few seconds and 1 minute. The preformed green body is compacted in a cold isostatic press at a pressure between 100 and 300 MPa. The pressure transmitting medium is water or oil.

(46) Subsequently, binding agent where required is burned away in a first thermal step. The duration and temperature of the heat treatment are in a range between 1 and 24 hours and temperatures between 600 and 1000° C. The burned green body is then sintered in a chamber furnace under oxygen flow. The sintering temperatures and durations are based on the sintering behavior of the mixture, that means once the composition has been defined, further compression into a ceramic of defined porosity is accomplished. In the case of Ce: Y.sub.3Al.sub.5O.sub.12 the garnet phase forms above about 1350 to 1450° C. Sintering into a ceramic body is accomplished at higher temperatures, between 1550° C. and 1800° C., for 2 to 24 hours.

(47) In this manner, optically translucent and homogeneous bodies are produced which may be further processed to converter materials.

(48) Example for Producing a Translucent (Y,Gd).sub.3Al.sub.5O.sub.12 Ceramic Including CeO.sub.2 by Uniaxial Compressing (with Reactive Sintering):

(49) Powders comprising primary particles having diameters of less than 1 μm, preferably of nanoscale size (<300 nm) in diameter, of Al.sub.2O.sub.3, Y.sub.2O.sub.3, Gd.sub.2O.sub.3, and CeO.sub.2 are weighed in proportions according to the target composition. The target composition may vary around the stoichiometric range of the garnet composition, i.e. may in particular extend by about 0.01 to 2.5 mol % to the Y.sub.2O.sub.3-rich side or by 0.01 to 2.5 mol % to the Al.sub.2O.sub.3-rich side. The Gd.sub.2O.sub.3 is set off against the Y.sub.2O.sub.3 content. The Gd.sub.2O.sub.3 content may amount to between 0 and 20% of Gd instead of Y, i.e. from 0 to 20% of the element A may be Gd. The CeO.sub.2 is stoichiometrically calculated to the Y site and ranges between 0.01 and 3 wt %. After addition of dispersing and binding agents, the mixture is blended in a ball mill using ethanol and Al.sub.2O.sub.3 balls, for 12 to 16 hours. Selectively, a second blending operation is performed in a tumbler for 10 to 24 h. Optionally, TEOS may be added to the mixture before the second blending operation as a sintering aid, so that the equivalent of between 0 and 0.5 wt % of SiO.sub.2 is employed.

(50) The milled suspension is selectively dried on a rotary evaporator or granulated in a spray dryer.

(51) The powder is then uniaxially compressed into plates or bars. Uniaxial pressure conditions are between 10 and 50 MPa, pressure durations between a few seconds and 1 minute. The preformed green body is compacted in a cold isostatic press at a pressure between 100 and 300 MPa. The pressure transmitting medium is water or oil.

(52) Subsequently, binding agent where required is burned away in a first thermal step. The duration and temperature of the heat treatment are in a range between 1 and 24 hours and temperatures between 600 and 1000° C. The burned green body is then sintered in a chamber furnace under oxygen flow, or selectively directly in air. The sintering temperatures and durations are based on the sintering behavior of the mixture, that means once the composition has been defined, further compression into a ceramic of defined porosity is accomplished. In the case of Ce: Y.sub.3Al.sub.5O.sub.12 the garnet phase forms above about 1350 to 1450° C. Sintering into a ceramic body is accomplished at higher temperatures, between 1550° C. and 1800° C., for 2 to 24 hours.

(53) In this manner, optically translucent and homogeneous bodies are produced which may be further processed to converter materials.

(54) Example for Producing a Translucent Lu.sub.3Al.sub.5O.sub.12 Ceramic by Uniaxial Compressing (with Reactive Sintering):

(55) Powders comprising primary particles having diameters of less than 1 μm, preferably of nanoscale size (<300 nm) in diameter, of Al.sub.2O.sub.3, Lu.sub.2O.sub.3, and CeO.sub.2 are weighed in proportions according to the target composition. The target composition may vary around the stoichiometric range of the garnet composition, i.e. may in particular extend by about 0.01 to 2.5 mol % to the Lu.sub.2O.sub.3.rich side or by 0.01 to 2.5 mol % to the Al.sub.2O.sub.3-rich side. The CeO.sub.2 is stoichiometrically calculated to the Y site and ranges between 0.01 and 3 wt %. After addition of dispersing and binding agents, the mixture is blended in a ball mill using ethanol and Al.sub.2O.sub.3 balls, for 12 to 16 hours. Prior to a second blending operation in a tumbler for 10 to 24 h, TEOS may be added to the mixture as a sintering aid, so that the equivalent of between 0 and 0.5 wt % of SiO.sub.2 is employed.

(56) The milled suspension is selectively dried on a rotary evaporator or granulated in a spray dryer.

(57) The powder is then uniaxially compressed into plates or bars. Uniaxial pressure conditions are between 10 and 50 MPa, pressure durations between a few seconds and 1 minute. The preformed green body is compacted in a cold isostatic press at a pressure between 100 and 300 MPa. The pressure transmitting medium is water or oil.

(58) Subsequently, binding agent where required is burned away in a first thermal step. The duration and temperature of the heat treatment are in a range between 1 and 24 hours and temperatures between 600 and 1000° C. The burned green body is then sintered in a chamber furnace under oxygen flow, or selectively directly in air. The sintering temperatures and durations are based on the sintering behavior of the mixture, that means once the composition has been defined, further compression into a ceramic of defined porosity is accomplished. In the case of Ce: Y.sub.3Al.sub.5O.sub.12 the garnet phase forms above about 1350 to 1450° C. Sintering into a ceramic body is accomplished at higher temperatures, between 1550° C. and 1800° C., for 2 to 24 hours.

(59) In this manner, optically translucent and homogeneous bodies are produced which may be further processed to converter materials.

(60) Example for Producing a Translucent (Y,Lu).sub.3Al.sub.5O.sub.12 Ceramic Including CeO.sub.2 by Uniaxial Compressing (with Reactive Sintering):

(61) Powders comprising primary particles having diameters of less than 1 μm, preferably of nanoscale size (<300 nm) in diameter, of Al.sub.2O.sub.3, Y.sub.2O.sub.3, Lu.sub.2O.sub.3, and CeO.sub.2 are weighed in proportions according to target composition. The target composition may vary around the stoichiometric range of the garnet composition, i.e. may in particular extend by about 0.01 to 2.5 mol % to the Y.sub.2O.sub.3-rich side or by 0.01 to 2.5 mol % to the Al.sub.2O.sub.3-rich side. The Lu.sub.2O.sub.3 is set off against the Y.sub.2O.sub.3 content. The Lu.sub.2O.sub.3 content may amount to between 100% and 50% of Lu instead of Y. The CeO.sub.2 is stoichiometrically calculated to the Lu site and ranges between 0.01 and 3 wt %. After addition of dispersing and binding agents, the mixture is blended in a ball mill using ethanol and Al.sub.2O.sub.3 balls, for 12 to 16 hours. Selectively, a second blending operation is performed in a tumbler for 10 to 24 h. Optionally, TEOS may be added to the mixture before the second blending operation as a sintering aid, so that the equivalent of between 0 and 0.5 wt % of SiO.sub.2 is employed.

(62) The milled suspension is selectively dried on a rotary evaporator or granulated in a spray dryer.

(63) The powder is then uniaxially compressed into plates or bars. Uniaxial pressure conditions are between 10 and 50 MPa, pressure durations between a few seconds and 1 minute. The preformed green body is compacted in a cold isostatic press at a pressure between 100 and 300 MPa. The pressure transmitting medium is water or oil.

(64) Subsequently, binding agent where required is burned away in a first thermal step. The duration and temperature of the heat treatment are in a range between 1 and 24 hours and temperatures between 600 and 1000° C. The burned green body is then sintered in a chamber furnace under oxygen flow, or selectively directly in air. The sintering temperatures and durations are based on the sintering behavior of the mixture, that means once the composition has been defined, further compression into a ceramic of defined porosity is accomplished. In the case of Ce: Y.sub.3Al.sub.5O.sub.12 the garnet phase forms above about 1350 to 1450° C. Sintering into a ceramic body is accomplished at higher temperatures, between 1550° C. and 1800° C., for 2 to 24 hours.

(65) In this manner, optically translucent and homogeneous bodies are produced which may be further processed to converter materials.

(66) Example for Producing a Translucent Lu.sub.3(Al,Ga).sub.5O.sub.12 Ceramic Including CeO.sub.2 by Uniaxial Compressing (with Reactive Sintering):

(67) Powders comprising primary particles having diameters of less than 1 μm, preferably of nanoscale size (<300 nm) in diameter, of Al.sub.2O.sub.3, Ga.sub.2O.sub.3, Lu.sub.2O.sub.3, and CeO.sub.2, are weighed in proportions according to the target composition. The target composition may vary around the stoichiometric range of the garnet composition, and may in particular extend by about 0.01 to 2.5 mol % to the Lu.sub.2O.sub.3-rich side or by 0.01 to 2.5 mol % to the Al.sub.2O.sub.3/Ga.sub.2O.sub.3-rich side. The CeO.sub.2 is stoichiometrically calculated to the Lu site and ranges between 0.01 and 3 wt %. The Ga.sub.2O.sub.3 content is set off against the Al.sub.2O.sub.3 content and is between 0 and 20%. After addition of dispersing and binding agents, the mixture is mixed in a ball mill using ethanol and Al.sub.2O.sub.3 balls, for 12 to 16 hours. Prior to a second blending operation in a tumbler for 10 to 24 h, TEOS may be added to the mixture as a sintering aid, so that the equivalent of between 0 and 0.5 wt % of SiO.sub.2 is employed.

(68) The milled suspension is selectively dried on a rotary evaporator or granulated in a spray dryer.

(69) The powder is then uniaxially compressed into plates or bars. Uniaxial pressure conditions are between 10 and 50 MPa, pressure durations between a few seconds and 1 minute. The preformed green body is compacted in a cold isostatic press at a pressure between 100 and 300 MPa. The pressure transmitting medium is water or oil.

(70) Subsequently, binding agent where required is burned out in a first thermal step. The duration and temperature of the heat treatment are in a range between 1 and 24 hours and temperatures between 600 and 1000° C. The burned green body is then sintered in a chamber furnace under oxygen flow, or selectively directly in air. The sintering temperatures and durations are based on the sintering behavior of the mixture, that means once the composition has been defined, further compression into a ceramic of defined porosity is accomplished. In the case of Ce: Y.sub.3Al.sub.5O.sub.12 the garnet phase forms above about 1350 to 1450° C. Sintering into a ceramic body is accomplished at higher temperatures, between 1550° C. and 1800° C., for 2 to 24 hours.

Exemplary Embodiments

(71) Specific embodiments of the invention are listed as exemplary embodiments in table 3.

(72) TABLE-US-00003 TABLE 3 Reactant Reactant Reactant Active Blending Exemplary 1 2 3 element in roller Blending in Sintering embodiment (mol %) (mol %) (mol %) (wt %) bench tumbler Aid 1 37.41 62.50 0.1 wt % 16 h 16 h Non Y.sub.2O.sub.3 Al.sub.2O.sub.3 CeO.sub.2 2 37.29 62.50 0.23 wt % 2 × 16 h 0.6 wt % Y.sub.2O.sub.3 Al.sub.2O.sub.3 Pr.sub.6O.sub.11+ TEOS 0.2 wt % CeO.sub.2 3 37.47 56.15 6.25 0.1 wt % 2 × 16 h 0.6 wt % Lu.sub.2O.sub.3 Al.sub.2O.sub.3 Ga.sub.2O.sub.3 CeO.sub.2 TEOS 4 37.22 62.50 0.19 0.1 wt % 16 h 16 h non Y.sub.2O.sub.3 Al.sub.2O.sub.3 Gd.sub.2O.sub.3 CeO.sub.2 5 37.33 56.18 6.24 0.2 wt % 2 × 16 h non Lu.sub.2O.sub.3 Al.sub.2O.sub.3 Ga.sub.2O.sub.3 CeO.sub.2 6 36.48 62.50 0.94 0.1 wt % 16 h 16 h non Y.sub.2O.sub.3 Al.sub.2O.sub.3 Gd.sub.2O.sub.3 CeO.sub.2 7 37.46 49.98 12.50  0.05 wt % 2 × 16 h 0.6 wt % Lu.sub.2O.sub.3 Al.sub.2O.sub.3 Ga.sub.2O.sub.3 CeO.sub.2 TEOS 8 33.67 62.50 3.75 0.1 wt % 16 h 16 h non Y.sub.2O.sub.3 Al.sub.2O.sub.3 Gd.sub.2O.sub.3 CeO.sub.2 9 18.7  62.50 18.7  0.1 wt % 2 × 16 h 0.6 wt % Y.sub.2O.sub.3 Al.sub.2O.sub.3 Lu.sub.2O.sub.3 CeO.sub.2 TEOS 10 37.46 62.50 0.05 wt % 24 h 0.3 wt % Y.sub.2O.sub.3 Al.sub.2O.sub.3 CeO.sub.2 TEOS 11 35.54 62.50 1.87 0.1 wt % 16 h 16 h non Y.sub.2O.sub.3 Al.sub.2O.sub.3 Gd.sub.2O.sub.3 CeO.sub.2 12 37.41 59.34 3.12 0.1 wt % 2 × 16 h 0.6 wt % Lu.sub.2O.sub.3 Al.sub.2O.sub.3 Ga.sub.2O.sub.3 CeO.sub.2 TEOS 13 29.92 62.50 7.49 0.1 wt % 16 h 16 h non Y.sub.2O.sub.3 Al.sub.2O.sub.3 Gd.sub.2O.sub.3 CeO.sub.2 14 37.56 62.40 0.05 wt % 16 h 16 h 0.6 wt % Y.sub.2O.sub.3 Al.sub.2O.sub.3 CeO.sub.2 TEOS