Manufacturing method for rare earth garnet type transparent ceramics

Abstract

To provide a method for producing a rare-earth garnet-type transparent ceramic, capable of high transparency with good reproducibility even in a ceramic with a garnet structure, which requires strict composition control.SOLUTION: A method for producing a rare-earth garnet-type transparent ceramic includes: weighing at least one oxide powder selected from Sc, Y, and lanthanide elements and one oxide powder selected from group 13 elements, under a respective inert gas atmosphere and with a mass loss of each oxide powder corrected based on a mass loss rate at 1,100°C; and using them as starting materials to produce the rare earth Garnet-type transparent ceramic.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing rare earth garnet-type transparent ceramics. [Background technology]

[0002] Ceramics have been widely used in daily life for a long time, such as tiles and pottery. Most ceramics are opaque, but in recent years, it has become possible to produce transparent ceramics with an optically isotropic crystal structure, transparency comparable to that of single crystals, by thoroughly removing air bubbles and minimizing the occurrence of heterogeneous phases at grain boundaries. Transparent ceramics are being developed into laser materials, scintillator materials, phosphors, magneto-optical elements, highly durable windows, etc., and are expected to become new optical materials different from single crystals.

[0003] Transparent ceramics must have an optically isotropic crystal structure, and examples of transparent ceramics include C-type rare earth structures, garnet structures, pyrochlore structures, and spinel structures. Among these, the garnet structure is particularly used in a wide range of fields, including YAG:Ce phosphors, TGG magneto-optical elements, and Nb:YAG lasers. On the other hand, the garnet structure is 3 B 5 O 12 Even the slightest deviation from the composition is not permitted, and there is a document that states that a deviation of about 0.2% from the stoichiometric composition reduces light transmittance (XW Ba, et al., J. Eur. Ceram. Soc. 35(2015)3127-3136 (Non-Patent Document 1)). Weighing out and mixing the ingredients according to the composition of the garnet structure is the first step in creating highly transparent garnet-type ceramics.

[0004] Here, methods for producing garnet-type transparent ceramics can be broadly divided into two types. In JP 2019-199386 A (Patent Document 1), high-quality YAG ceramics are achieved by mixing various raw material powders, molding, and sintering the mixture. Furthermore, in Japanese Patent No. 6438588 (Patent Document 2), the synthesis of highly transmittance garnet-type transparent ceramics is achieved by synthesizing precursor solutions of various elements through a coprecipitation process, rather than by mixing powders. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-199386 A [Patent Document 2] Patent No. 6438588 [Non-patent literature]

[0006] [Non-Patent Document 1] XW Ba, et al., J. Eur. Ceram. Soc. 35(2015)3127-3136 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the production of ceramics in Patent Document 1, each type of raw material powder has its own specific surface area and the amount of moisture adsorbed on the surface is different. In addition to the amount of moisture, depending on the synthesis method of the powder, it may contain components (impurity components) that are unrelated to the main component, such as organic matter, nitrides, and sulfides. Furthermore, for example, Tb oxide is Tb at room temperature. 2 O 3 The state of Tb is unstable. 4 O 7 However, the Tb oxide is not truly Tb. 4 O 7There is no guarantee that the composition of the raw material powder is the same as that of the raw material powder, and the composition may vary significantly depending on the manufacturer, the manufacturing method, or the storage method. Therefore, even if such raw material powder is weighed according to the target composition, the composition of the sintered body produced may deviate, resulting in a situation where the sintered body is not transparent or does not have high transmittance. In such a case, it is possible to manufacture highly transparent garnet-type transparent ceramics by determining the weighing amounts of various powders through trial and error, but it is difficult to obtain the exact same powder, such as a powder with the same specific surface area, again. When raw material powder from a different production lot is used, such as when a certain type of raw material powder runs out of stock and is replaced with a new powder, it is necessary to adjust the weighing conditions again. The advantage of the coprecipitation process in Patent Document 2 is that not only can a completely uniform powder be obtained, but also that there is no need to consider the effects of surface adsorbed water, as in the case of powder mixing. However, due to errors in measuring the concentration of the precursor solution and errors in weighing, there was no guarantee that the composition would be completely as desired. In the end, there was no way to avoid finding the conditions for achieving transparency through trial and error, just like in the case of manufacturing by mixing the raw material powders described above.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing rare earth garnet-type transparent ceramics which is capable of imparting a high degree of transparency with good reproducibility even to garnet-structure ceramics which require strict composition control. [Means for solving the problem]

[0009] In order to achieve the above object, the present invention provides the following method for producing a rare earth garnet-type transparent ceramic. 1. Using as starting materials at least one oxide powder selected from Sc, Y and lanthanoid elements and one oxide powder selected from Group 13 elements, a compound represented by the following formula (1) was prepared. (A 1 1-x-y A 2 x Sc y ) 3 (B 1-z Scz ) 5 O 12 (1) (In formula (1), A 1 , A 2 are elements different from each other selected from Y and the lanthanoid elements, B is one selected from the Group 13 elements, 0≦x≦0.4, 0≦y<0.08, 0≦z<0.16, and when z=0, y=0, and when z>0, y>0. A method for producing a rare earth garnet-type transparent ceramic, which is a sintered body of a complex oxide represented by the following formula: Above A 1 、A 2 are elements different from each other selected from Tb, Y, Ce, Lu and Dy, B is Al, As the starting material, Tb, each with a purity of 99.9 mass% or more; Y , Ce, Lu and Dy The powder of oxides of different elements selected from the following is mixed with mass m A1 , m A2 Weigh only Al with a purity of 99.9% by mass or more The mass m of the oxide powder is calculated by the following formula (2-3). B Weigh only Purity of 99.9% by mass or more The mass m of scandium oxide powder is calculated using the following formula (2-4). Sc The method for producing rare earth garnet-type transparent ceramics is as follows: m A1 =3 / 2×(1-xy)M A1 / M G ×W×100 / (100-a A1 ) (2-1) m A2 =3 / 2×xM A2 / M G ×W×100 / (100-a A2 ) (2-2) m B =5 / 2×(1-z)M B / M G ×W×100 / (100-a B ) (2-3) m Sc =(3y / 2+5z / 2)(M Sc / M G)×W×100 / (100-a Sc ) (2-4) (In the formula, M A1 , M A2 teeth Tb, Y , Ce, Lu and Dy are the molar masses (g / mol) of oxides of different elements selected from B teeth Al is the molar mass of the oxide (g / mol), and M Sc is the molar mass of scandium oxide (g / mol), M G is the molar mass (g / mol) of the composite oxide represented by formula (1), W is the planned total mass (g) of the above starting materials, and a A1 , a A2 is the starting material Tb, Y , Ce, Lu and Dy is the mass reduction rate (%) when oxide powders of different elements selected from the following are heated in an inert gas atmosphere from room temperature (20±10°C) to 1100°C; B is the starting material Al is the mass loss rate (%) when the oxide powder is heated from room temperature (20±10℃) to 1100℃ in an inert gas atmosphere, and a Sc is the mass loss rate (%) when the starting scandium oxide powder is heated from room temperature (20±10°C) to 1100°C in an inert gas atmosphere. x, y, and z are the same as above. 2 . The sintered body is treated with SiO 2 Contains more than 0 mass% and 0.1 mass% or less 1 to The method for producing the rare earth garnet-type transparent ceramics described above. 3 . A in the above formula (1) 1 is Tb, and 0.6≦1-xy≦1. or 2 2. A method for producing the rare earth garnet-type transparent ceramics according to claim 1 . 4 . After the starting materials are molded, the molded body is degreased and sintered to obtain a sintered body of the composite oxide. 3 13. A method for producing the rare earth garnet-type transparent ceramic according to any one of claims 1 to 12. Effect of the Invention

[0010] According to the present invention, when starting powders are mixed as raw materials to produce transparent ceramics consisting of a sintered body of a composite oxide, the amount required corresponding to the ceramic composition can be accurately weighed by correcting the mass used based on the amount of adsorbate not contributing to the ceramic composition, which is previously measured for each starting raw material powder, and therefore rare earth garnet-type transparent ceramics with high transparency can be produced with good reproducibility. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of the configuration of an optical isolator using the transparent ceramic produced in accordance with the present invention as a Faraday rotator. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] A method for producing the rare earth garnet-type transparent ceramics according to the present invention will now be described.

[0013] The method for producing a rare earth garnet-type transparent ceramic according to the present invention comprises using, as starting materials, a powder of at least one oxide selected from Sc, Y and a lanthanoid element, and a powder of one oxide selected from a group 13 element, and reacting the powder with an oxide represented by the following formula (1): (A 1 1-x-y A 2 x Sc y ) 3 (B 1-z Sc z ) 5 O 12 (1) (In formula (1), A 1 , A 2 are elements different from each other selected from Y and the lanthanoid elements, B is one selected from the Group 13 elements, 0≦x≦0.4, 0≦y<0.004, 0≦z<0.004, when z=0, y=0, and when z>0, y>0. A method for producing a rare earth garnet-type transparent ceramic, which is a sintered body of a complex oxide represented by the following formula: As the starting material, powders of oxides of different elements selected from Y and lanthanoid elements are used in an amount of m calculated by the following formulas (2-1) and (2-2): A1 , m A2 The powder of one oxide selected from the group 13 elements is weighed out, and the mass m B The scandium oxide powder is weighed out and the mass m Sc The present invention is characterized in that only the amount of the component is weighed out and used. m A1 =3 / 2×(1-xy)M A1 / M G ×W×100 / (100-a A1 ) (2-1) m A2 =3 / 2×xM A2 / M G ×W×100 / (100-a A2 ) (2-2) m B =5 / 2×(1-z)M B / M G ×W×100 / (100-a B ) (2-3) m Sc =(3y / 2+5z / 2)(M Sc / M G )×W×100 / (100-a Sc ) (2-4) (In the formula, M A1 , M A2 is the molar mass (g / mol) of the oxide of each of the elements different from each other selected from Y and the lanthanoid elements, and M B is the molar mass (g / mol) of one oxide selected from Group 13 elements, and M Sc is the molar mass of scandium oxide (g / mol), M G is the molar mass (g / mol) of the composite oxide represented by formula (1), W is the planned total mass (g) of the above starting materials, and a A1 , a A2is the mass loss rate (%) when the starting material oxide powders of different elements selected from Y and lanthanoid elements are heated from room temperature (20±10°C) to 1100°C in an inert gas atmosphere, and a B is the mass loss rate (%) when the starting material oxide powder selected from the group 13 elements is heated from room temperature (20±10°C) to 1100°C in an inert gas atmosphere, and a Sc is the mass loss rate (%) when the starting scandium oxide powder is heated from room temperature (20±10°C) to 1100°C in an inert gas atmosphere. x, y, and z are the same as above.

[0014] (Rare earth garnet type transparent ceramics) The rare earth garnet-type transparent ceramics (hereinafter sometimes simply referred to as transparent ceramics) produced in the present invention are transparent sintered bodies of a complex oxide represented by the following formula (1). (A 1 1-x-y A 2 x Sc y ) 3 (B 1-z Sc z ) 5 O 12 (1) (In formula (1), A 1 , A 2 are elements different from each other selected from Y and the lanthanoid elements, B is one selected from the Group 13 elements, 0≦x≦0.4, 0≦y<0.004, 0≦z<0.004, when z=0, y=0, and when z>0, y>0.

[0015] In the garnet crystal structure represented by formula (1), element A 1 , A 2 The side where element B, Sc is coordinated, i.e., the side in the parentheses on the left side of formula (1), is called the A site, and the side where element B, Sc is coordinated, i.e., the side in the parentheses on the right side of formula (1), is called the B site.

[0016] Here, deviations in the composition ratio of the A site and the B site (i.e., 3:5) in the ceramics actually manufactured are not permitted. Even if the composition ratio in the manufactured ceramics deviates slightly, it may become transparent, but the transparency will be poor. The garnet structure of the ceramics cannot achieve a high degree of transparency unless its composition is as desired, so it is necessary to satisfy formula (1).

[0017] Moreover, the transparent ceramics produced by the present invention is preferably a sintered body of a garnet-type composite oxide containing at least terbium (Tb) and aluminum (Al). In this case, the element B in the above formula (1) is Al. Furthermore, SiO 2 It is more preferable that the content be more than 0 mass % and 0.1 mass % or less.

[0018] In addition, A in the above formula (1) 1 is Tb, and 0.6≦1-xy≦1 is preferable. When Tb is contained at 40 mol% or more in the A site of formula (1), the obtained transparent ceramic is used as a magneto-optical element. Tb is an element with the largest Verdet constant among the paramagnetic elements except for iron (Fe), and has no absorption in the 1064 nm wavelength region used in fiber lasers, so it is the most suitable element for use as an optical isolator material in this wavelength region. However, Tb easily reacts with oxygen in the air to generate tetravalent Tb. This tetravalent Tb has light absorption properties, so it is desirable to eliminate it as much as possible. To completely eliminate this tetravalent Tb, it is necessary to aim for a crystal structure in which tetravalent Tb does not generate, and it is most preferable to aim for a composition that forms a garnet structure.

[0019] When Tb is included in the A site of formula (1), it is possible to make the crystal transparent with Tb alone, but Tb may be substituted with other elements to make the crystal transparent. The element substituted for Tb is preferably at least one selected from the group of Y or lanthanoids, and Y, Lu, or La is preferable from the viewpoint of no absorption in the wavelength band used, and Y is the most preferable from the viewpoint of cost and stability. Y is an element that stabilizes the garnet structure, and the more it is substituted, the more stable it becomes and the easier it is to manufacture. However, if too much is added, the Verdet constant becomes too small, and the Verdet constant becomes smaller than that of TGG. Therefore, it is preferable to substitute Y in the range of 0 mol% to 40 mol% with respect to 100 mol% of Tb.

[0020] At the B site of formula (1), one element (element B) selected from the group 13 elements is placed, with Al being preferred as mentioned above. Ga, a group 13 element, is highly volatile and volatilizes during sintering, reducing its amount, so special measures are required, but Al does not volatilize during sintering and has high thermal conductivity, making it the most preferred.

[0021] Here, in a composite oxide whose constituent elements are only Tb, Y, a lanthanoid element, and a group 13 element, a garnet structure may not be obtained due to a slight weighing error of each raw material, and it is difficult to stably manufacture a transparent ceramic usable for optical applications. Therefore, in the present invention, it is preferable to eliminate the composition deviation due to a slight weighing error of each raw material by adding scandium (Sc) as a constituent element. Sc is a material having an intermediate ionic radius that can be dissolved in both the A site and the B site in an oxide having a garnet structure, and is a buffer material that can adjust the distribution ratio to the A site (rare earth site consisting of Tb, Y, and a lanthanoid element) and the B site (site consisting of a group 13 element) to exactly match the stoichiometric ratio and thereby minimize the energy of crystallite formation when the compounding ratio of the rare earth elements consisting of Tb, Y, and a lanthanoid element and the group 13 element deviates from the stoichiometric ratio due to the variation in weighing.

[0022] The content of Sc is preferably 0 mol% or more and less than 0.08 mol% at the A site, and preferably 0 mol% or more and less than 0.16 mol% at the B site. When it is highly transparent without adding Sc, there is no particular need to add it, but it is preferably added to some extent from the perspective of stable production. On the other hand, if it is above the upper limit of the content, it will be easier to achieve transparency, but a large amount of expensive Sc will be used, resulting in an uneconomical cost, so it is not preferable.

[0023] Based on the above, the transparent ceramics produced in the present invention are preferably a transparent sintered body of a composite oxide represented by the following formula (1’). (Tb 1-x’-y’ Y x’ Sc y’ ) 3 (Al 1-z’ Sc z’ ) 5 O 12 (1’) (In the formula, 0.05 ≦ x’ ≦ 0.4, 0 ≦ y’ < 0.08, 0.52 ≦ 1 - x’ - y’ < 0.95, 0 ≦ z’ < 0.16, 0.001 < y’ + z’ < 0.2.)

[0024] In formula (1’), the range of x’ is 0.05 ≦ x’ ≦ 0.4, preferably 0.1 ≦ x’ ≦ 0.4, and more preferably 0.2 ≦ x’ ≦ 0.4. When x’ is in this range, the perovskite-type heterogeneous phase can be reduced to a level where it cannot be detected by X-ray diffraction (XRD) analysis.

[0025] In formula (1’), the range of y’ is 0 ≦ y’ < 0.08, preferably 0.001 < y’ < 0.04, and more preferably 0.002 < y’ < 0.04. When y’ is in this range, it is preferable because the perovskite-type heterogeneous phase can be reduced to a level where it cannot be detected by X-ray diffraction (XRD) analysis. Furthermore, it is preferable because it can prevent an excessive decrease in the thermal conductivity caused by the homogeneity of the sintered body and grain boundary scattering.

[0026] In formula (1’), the range of 1 - x’ - y’ is 0.52 ≦ 1 - x’ - y’ < 0.95, and more preferably 0.6 ≦ 1 - x’ - y’ < 0.8. When 1 - x’ - y’ is within this range, a large Verdet constant can be ensured and high transparency can be obtained at a wavelength of 1064 nm.

[0027] In formula (1’), the range of z’ is 0 ≦ z’ < 0.16, more preferably 0.001 < z’ < 0.004, and even more preferably 0.02 ≦ z’ < 0.004. When z’ is within this range, it is preferable because the perovskite-type heterophase can be reduced to a level where it cannot be detected by X-ray diffraction (XRD) analysis. Furthermore, it is preferable because it can prevent an excessive decrease in the thermal conductivity due to the homogeneity of the sintered body and grain boundary scattering.

[0028] In formula (1’), the range of y’ + z’ is 0.001 < y’ + z’ < 0.2, more preferably 0.002 < y’ + z’ < 0.03, and even more preferably 0.003 < y’ + z’ < 0.025. When y’ + z’ is within this range, it is preferable because the perovskite-type heterophase can be reduced to a level where it cannot be detected by X-ray diffraction (XRD) analysis. Furthermore, it is preferable because it can prevent an excessive decrease in the thermal conductivity due to the homogeneity of the sintered body and grain boundary scattering.

[0029] The transparent ceramics produced by the present invention contain, as a main component, the complex oxide represented by the above formula (1) or formula (1’), and as a sub-component, SiO which serves as a sintering aid 2 in a range of 0.1 mass% or less in terms of metallic Si. When a small amount of SiO 2 is added as a sintering aid, the precipitation of perovskite-type heterophases, alumina heterophases, etc. is suppressed, so the transparency of the paramagnetic garnet-type transparent ceramics is further improved. Furthermore, the slightly added SiO 2 is vitrified during sintering at 1400 °C or higher to bring about a liquid-phase sintering effect, and can promote the densification of the garnet-type ceramic sintered body.

[0030] Incidentally, "containing as a main component" means containing 90% by mass or more of the composite oxide represented by the above formula (1) or formula (1'). The content of the composite oxide represented by formula (1) or formula (1') is preferably 99% by mass or more, more preferably 99.9% by mass or more, even more preferably 99.99% by mass or more, and particularly preferably 99.999% by mass or more.

[0031] The transparent ceramics produced by the present invention are composed of the above-mentioned main components and subcomponents, but may further contain other elements within a range that does not impair the effects of the present invention. Typical examples of other elements include heavy metals such as iron (Fe) and chromium (Cr), and various impurities (unavoidable components) such as sodium (Na), potassium (K), and phosphorus (P). The content of other elements in the sintered body is preferably 100 ppm or less.

[0032] By the way, when preparing raw material powders for transparent ceramics, there are two methods: mixing various oxide powders and synthesizing uniform oxide powders from an aqueous solution using a chemical reaction. The present invention relates to the former manufacturing method of mixing various oxide powders. Various oxide powders contain components other than the constituent oxides, such as adsorbed moisture according to their specific surface area, residual organic matter derived from the synthesis method of the starting materials, and nitrides, and the ratio of these components varies depending on the oxide powder. Due to the influence of components other than the constituent oxides, even if the oxide powder is weighed according to the target composition, the composition of the manufactured ceramics will vary, and a high level of transparency will not be achieved. In the present invention, the above rare earth garnet-type transparent ceramics are produced as follows.

[0033] [Manufacturing method for rare earth garnet-type transparent ceramics] (Starting material) As the starting material used in the present invention, a single oxide powder of each of the elements constituting the above formula (1) is used. For example, in the case of a composite oxide represented by formula (1'), each oxide powder of terbium, yttrium, scandium, and aluminum (i.e., terbium oxide powder, yttrium oxide powder, scandium oxide powder, and aluminum oxide powder) is used. These are called raw material powders for garnet-type composite oxides. The purity of the raw material powder for garnet-type composite oxides is preferably 99.9% by mass or more, and particularly preferably 99.99% by mass or more. Hereinafter, an example will be described in which terbium oxide powder, yttrium oxide powder, scandium oxide powder, and aluminum oxide powder corresponding to the composite oxide represented by formula (1') are used.

[0034] In the present invention, the starting materials terbium oxide powder, yttrium oxide powder, scandium oxide powder and aluminum oxide powder are precisely weighed to obtain the composite oxide composition represented by the above formula (1'), but since these starting oxide powders contain components other than the constituent oxides as described above, the starting oxide powders are weighed in consideration of the content of the components other than the constituent oxides in each of the starting oxide powders. Specifically, the following is carried out.

[0035] (Measurement of mass reduction rate of oxide powder at 1100℃ (content of components other than constituent oxides)) In the present invention, as a method for measuring the content (weight ratio) of components other than the above-mentioned constituent oxides in the starting oxide powder, it is preferable to measure the thermogravimetric change rate under an inert atmosphere. The thermogravimetric change rate can be measured in-situ using a thermogravimetric analyzer (TG apparatus) or by measuring the weight before and after firing at 1000°C or higher using a firing furnace. However, since it is necessary to accurately measure the weight of components other than the constituent oxides, it is most preferable to measure using a TG apparatus. The atmosphere is preferably an inert atmosphere, and examples thereof include argon, nitrogen, and helium, but there is no particular limitation as long as the weight change rate can be accurately measured.

[0036] Here, the weight loss rate (mass loss rate) using a TG device is preferably calculated from the weight change (mass loss) when heated from room temperature (20±10° C.) to 1100° C. At temperatures lower than 1100° C., residual adsorbed moisture and Tb 4 O 7 In the case of 1100°C, residual oxygen remains, making it impossible to capture the correct weight change, and the composition may not match. The mass loss at temperatures higher than 1100°C, for example 1300°C, is not much different from that at 1100°C for most oxides, but Ga 2 O 3 For highly volatile oxides such as those mentioned above, an excessive mass loss due to volatilization may be observed at 1300°C. As a result of the inventors' investigation into the temperature at which the mass loss rate of all oxides of the framework elements of rare earth garnets can be measured with high accuracy, it was found that 1100°C is the most preferable heating temperature. That is, the "mass loss rate at 1100°C" in the present invention refers to the ratio (%) of mass loss of the oxide powder, which is the starting material, relative to the mass (100%) at room temperature (20±10°C) when the oxide powder is heated from room temperature (20±10°C) to 1100°C under an inert atmosphere.

[0037] In the present invention, the mass reduction rate at 1100° C. is measured for each of all oxide powders used as starting materials (terbium oxide powder, yttrium oxide powder, scandium oxide powder, and aluminum oxide powder).

[0038] (Calculation of mass used) The mass of the oxide powder used as the starting material is calculated using the mass reduction rate of each oxide powder measured as above. Note that the molecular structure of the oxide in the oxide powder is always A 1 2 O 3 , A 2 2 O 3 , B 2 O 3 , Sc 2 O 3 For example, Tb oxide is calculated as Tb 4 O 7In this calculation, it is sold as Tb 4 O 7 Since this does not hold, Tb 2 O 3 It is necessary to calculate it.

[0039] That is, as the starting material, the mass m of "powder of oxides of different elements selected from Y and lanthanoid elements" is used. A1 , m A2 is calculated from the following formulas (2-1) and (2-2). In addition, the mass m B is calculated from the following formula (2-3). Furthermore, the mass m Sc is calculated from the following formula (2-4). m A1 =3 / 2×(1-xy)M A1 / M G ×W×100 / (100-a A1 ) (2-1) m A2 =3 / 2×xM A2 / M G ×W×100 / (100-a A2 ) (2-2) m B =5 / 2×(1-z)M B / M G ×W×100 / (100-a B ) (2-3) m Sc =(3y / 2+5z / 2)(M Sc / M G )×W×100 / (100-a Sc ) (2-4) (In the formula, M A1 , M A2 is the molar mass (g / mol) of the oxide of each of the elements different from each other selected from Y and the lanthanoid elements, and M B is the molar mass (g / mol) of one oxide selected from Group 13 elements, and M Sc is the molar mass of scandium oxide (g / mol), M Gis the molar mass (g / mol) of the composite oxide represented by formula (1), W is the planned total mass (g) of the above starting materials, and a A1 , a A2 is the mass loss rate (%) when the starting material oxide powders of different elements selected from Y and lanthanoid elements are heated from room temperature (20±10°C) to 1100°C in an inert gas atmosphere, and a B is the mass loss rate (%) when the starting material oxide powder selected from the group 13 elements is heated from room temperature (20±10°C) to 1100°C in an inert gas atmosphere, and a Sc is the mass loss rate (%) when the starting scandium oxide powder is heated from room temperature (20±10°C) to 1100°C in an inert gas atmosphere. x, y, and z are the same as x, y, and z in the above formula (1).

[0040] In addition, in the composite oxide represented by formula (1), when element A2 is not included (x=0), m A2 = 0, and if Sc is not included (y = z = 0), m Sc =0.

[0041] When terbium oxide powder, yttrium oxide powder, scandium oxide powder, and aluminum oxide powder are used as the starting materials, the mass m of the terbium oxide powder used is Tb , the mass of yttrium oxide powder used m Y , the mass of aluminum oxide powder used m AL , the mass of scandium oxide powder used m Sc can be calculated using the following formula: m Tb =3 / 2×(1-x'-y')M Tb / M G ×W×100 / (100-a Tb ) m Y =3 / 2×x'M Y / M G ×W×100 / (100-a Y ) m AL =5 / 2×(1-z')M AL / MG ×W×100 / (100-a Al ) m Sc =(3y' / 2+5z' / 2)(M Sc / M G )×W×100 / (100-a Sc ) (In the formula, M Tb , M Y is the molar mass of the oxides of Tb and Y (M Tb = 365.8 (g / mol), M Y = 225.8 (g / mol)), and M AL is the molar mass of Al oxide (M AL = 102.0 (g / mol)), and M Sc is the molar mass of scandium oxide (M Sc = 137.9 (g / mol)), and M G is the molar mass (g / mol) of the composite oxide represented by formula (1'), W is the planned total mass (g) of the above starting materials, and a Tb , a Y is the mass loss rate (%) when the starting material Tb and Y oxide powders are heated from room temperature (20±10°C) to 1100°C in an inert gas atmosphere, and a Al is the mass loss rate (%) when the starting Al oxide powder is heated from room temperature (20±10°C) to 1100°C in an inert gas atmosphere, and a Sc is the mass loss rate (%) when the starting scandium oxide powder is heated from room temperature (20±10°C) to 1100°C in an inert gas atmosphere. x', y', and z' are the same as x', y', and z' in the above formula (1').

[0042] (Weighing) Based on the masses used calculated as above, each of the oxide powders as starting materials is precisely weighed using a precision balance capable of measuring to four decimal places.

[0043] (Mixing process) The weighed oxide powder, which is the starting material, is mixed uniformly, and if necessary, the powder that has aggregated to become secondary particles is pulverized to the state of primary particles, so that a mixing process is performed. There are wet and dry mixing processes, but there is no particular limitation as long as the powder can be mixed uniformly. In addition, in the wet process, examples include ball mills, jet mills, bead mills, ultrasonic dispersion, and homogenizer processing, and examples of the dispersion medium include water, methanol, ethanol, propyl alcohol, or a dispersion medium obtained by mixing them in any ratio. In order to increase the efficiency of the mixing process, an organic dispersant may be added, and examples of the organic dispersant include polyethylene glycol-based dispersants, sulfonic acid-based dispersants, and phosphoric acid-based dispersants. A binder required to improve the shape retention in the subsequent molding process is added at the stage of this mixing process. It is essential to select a binder structure that dissolves in the dispersion medium. When the dispersion medium is water, a polyvinyl alcohol-based binder is exemplified, and when the dispersion medium is a lower alcohol such as ethanol, examples of the binder include polyvinyl butyral, polyvinyl acetate, or copolymers thereof. The amount of addition is not particularly limited as long as the shape retention is maintained in the subsequent molding process.

[0044] In addition, SiO 2 When adding SiO 2 The raw material is, for example, tetraethyl orthosilicate (TEOS) or silicon oxide powder, such as SiO 2 The raw material is preferably tetraethyl orthosilicate (TEOS), and the amount of the raw material to be added is SiO 2 The amount is more than 0 ppm and less than 1,000 ppm (more than 0 mass% and less than 0.1 mass%) in the whole raw powder (raw powder for garnet-type composite oxide + sintering aid) when converted. 2 In the case of silicon oxide powder (SiO ), the amount is preferably more than 0 ppm and less than 1,000 ppm (more than 0 mass % and less than 0.1 mass %) in the entire raw powder (raw powder for garnet-type complex oxide + sintering aid). If the amount added is more than 1,000 ppm, there is a risk of slight light absorption occurring due to crystal defects caused by the excess Si. 2In the case of powder, the primary particle size is not particularly limited, but it is preferable to use fine powder of less than 1 μm, since the sintering aid can be uniformly dispersed in the starting material.

[0045] (molding process) After the mixing process, the mixture is molded into a desired shape. There are wet and dry molding methods, but there are no particular limitations as long as the mixture is molded into a desired shape. Examples of wet molding include casting, centrifugal casting, extrusion, and tape molding, and examples of dry molding include dry uniaxial press molding and cold isostatic pressing (CIP (Cold Isostatic Pressing)) molding. Two or more of these molding methods may be combined, and CIP molding may be performed after dry uniaxial press molding or CIP molding may be performed after casting. The relative density to the true density after molding is preferably 45% to 65%, more preferably 50% to 60%.

[0046] In the present invention, the starting materials, terbium oxide powder, yttrium oxide powder, scandium oxide powder and aluminum oxide powder, which are precisely weighed in the above-mentioned mixing step, and SiO 2 It is preferable to wet mix the raw material to form a slurry, spray dry the slurry to form a granular raw material, and then mold the granular raw material. In this case, a normal press molding process can be suitably used.

[0047] (Degreasing process) The obtained molded body contains a large amount of organic matter such as binder, so it is subjected to a degreasing treatment. The degreasing is preferably performed in an atmosphere of 18 vol% or more of oxygen, and the degreasing temperature and time are not particularly limited as long as the conditions are selected so that the organic matter can be completely decomposed, but are preferably 250°C or more, more preferably 300°C or more, and even more preferably 400°C or more. The upper limit of the degreasing temperature is preferably a temperature at which densification does not progress, and is preferably 1000°C or less. The degreasing time is preferably 1 hour or more and 24 hours or less.

[0048] (Sintering process) The degreased molded body is subjected to a sintering process to make it transparent. As a method of making it transparent by sintering, there is a method of making it transparent only by sintering under atmospheric pressure, and a method of making it transparent by pre-sintering it under atmospheric pressure to a relative density of 93% to 99% and then performing a hot isostatic pressing (HIP) process, and either method may be used in the present invention. The sintering temperature is not particularly limited as long as it is possible to achieve the desired sintered density or to make it highly transparent. In addition, the sintering atmosphere is not particularly limited as long as no bubbles remain when it is made transparent, and examples of the sintering atmosphere include a vacuum, an oxygen atmosphere, and air. When performing HIP processing, the pressure medium is preferably argon, nitrogen, or argon containing 1 vol% or less of oxygen, and the pressure is preferably 100 MPa to 200 MPa.

[0049] (Annealing process) The obtained sintered body may contain some oxygen deficiencies, so it is necessary to perform annealing treatment in an atmosphere with an oxygen content of 15 vol% or more. The annealing temperature is not particularly limited as long as the oxygen deficiencies are eliminated, but it is preferably 1200°C or more and 1500°C or less. If it is less than 1200°C, there is not enough heat to eliminate the oxygen deficiencies, while if it is more than 1500°C, it is not preferable because bubbles may re-occur due to annealing. The annealing time is also sufficient to eliminate the oxygen deficiencies, and it is preferably 20 hours or more and 100 hours or less.

[0050] (Processing process) In the manufacturing method of the present invention, it is preferable to optically polish both end faces on the optically utilized axis of the sintered body (rare earth garnet-type transparent ceramics) that has undergone the above-mentioned series of manufacturing steps. In this case, the optical surface precision is preferably λ / 8 or less, particularly preferably λ / 10 or less, when the measurement wavelength λ=633 nm. It is also possible to further reduce optical loss by appropriately forming an anti-reflection film on the optically polished surface.

[0051] In this manner, rare earth garnet-type transparent ceramics with high transparency can be obtained with good reproducibility. Also, a transparent ceramic usable as a high-output Faraday rotator can be obtained, which is made of a sintered body of a paramagnetic garnet-type composite oxide represented by formula (1') using terbium oxide powder, yttrium oxide powder, scandium oxide powder, and aluminum oxide powder as starting materials, and in which the absorption and scattering of light with a wavelength of 1064 nm at a mounting length of 20 mm is minimized.

[0052] [Magneto-optical devices] Furthermore, since the rare earth garnet-type transparent ceramic obtained in the present invention is assumed to be used as a magneto-optical material, it is preferable to apply a magnetic field parallel to the optical axis of the paramagnetic garnet-type transparent ceramic, and then set a polarizer and an analyzer so that their optical axes are shifted by 45 degrees from each other to form a magneto-optical device. That is, the magneto-optical material of the present invention is suitable for magneto-optical device applications, and is particularly suitable for use as a Faraday rotator for an optical isolator with a wavelength of 0.9 to 1.1 μm.

[0053] FIG. 1 is a schematic cross-sectional view showing an example of an optical isolator, which is an optical device having, as an optical element, a Faraday rotator made of the transparent ceramic obtained by the present invention. 1, an optical isolator 100 includes a Faraday rotator 110 made of the paramagnetic garnet-type transparent ceramic obtained in the present invention, and a polarizer 120 and an analyzer 130, which are polarizing materials, are provided in front of and behind the Faraday rotator 110. Moreover, it is preferable that the optical isolator 100 has the polarizer 120, the Faraday rotator 110, and the analyzer 130 arranged in this order on its optical axis, and that a magnet 140 is placed on at least one of the side surfaces of these elements.

[0054] The optical isolator 100 can be suitably used in industrial fiber laser devices, that is, to prevent the reflected light of the laser light emitted from the laser light source from returning to the light source, causing the oscillation to become unstable. EXAMPLES

[0055] EXAMPLES The present invention will be described in more detail below with reference to examples, comparative examples and reference examples, but the present invention is not limited to the examples.

[0056] [Test Example 1] (Measurement of mass loss rate of starting material at 1100℃) The mass loss rate at 1100°C of various oxide powders used as starting materials in this example was measured using a thermogravimetric / differential thermal analyzer (Thermo Plus Evo) manufactured by Rigaku Corporation. That is, the oxide powder was placed in a platinum container, and the weight of the powder was measured using a precision balance capable of measuring to the fourth decimal point. After accurately measuring the weight, the platinum container containing the starting material was set in the thermogravimetric / differential thermal analyzer. The atmosphere was He, and the material was heated from room temperature (20°C) to 1200°C at a heating rate of 15°C / min, and then air-cooled to room temperature, during which thermogravimetric (TG) measurements were performed. The mass loss rate at 1100°C was obtained from the measurement data, and this value was taken as a (%).

[0057] The details of the measured oxide powders are shown below. Tb 4 O 7 (Fine powder): Shin-Etsu Chemical Co., Ltd., large specific surface area type, particle size 180 nm, purity 99.9% by mass Y 2 O 3 (Fine powder): Shin-Etsu Chemical Co., Ltd., large specific surface area type, particle size 180 nm, purity 99.9% by mass ·Sc 2 O 3 Manufactured by Shin-Etsu Chemical Co., Ltd., particle size 3 μm, purity 99.9% by mass ·CeO 2 Manufactured by Shin-Etsu Chemical Co., Ltd., large specific surface area type, particle size 180 nm, purity 99.9% by mass Lu 2 O 3 Manufactured by Shin-Etsu Chemical Co., Ltd., large specific surface area type, particle size 180 nm, purity 99.9% by mass ·Dy 2 O 3Manufactured by Shin-Etsu Chemical Co., Ltd., large specific surface area type, particle size 180 nm, purity 99.9% by mass ·Al 2 O 3 Manufactured by Taimei Chemical Co., Ltd., Taimicron, particle size 300 nm, purity 99.9% by mass Tb 4 O 7 (Coarse powder): Shin-Etsu Chemical Co., Ltd., standard type, particle size 3 μm, purity 99.9% by mass Y 2 O 3 (Coarse powder): Shin-Etsu Chemical Co., Ltd., standard type, particle size 3 μm, purity 99.9% by mass

[0058] Table 1 shows the mass loss rate of the starting material (oxide powder) used in the present invention at 1100° C. It was found from Table 1 that the mass loss rate at 1100° C. varies greatly depending on the type of starting material, and each material has its own specific surface area and adsorbed components.

[0059] [Table 1]

[0060] [Example 1] Among the above starting materials, Tb 4 O 7 (fine powder), Y 2 O 3 (fine powder), Sc 2 O 3 , CEO 2 , Lu 2 O 3 , Dy 2 O 3 , Al 2 O 3 Using the above, transparent ceramics were produced in the following procedure.

[0061] (Weighing and raw material preparation process) For each target composition, the mass used was calculated as follows using the mass loss rate a (%) at 1100°C measured in Test Example 1. Note that the planned total mass W of the starting materials was 50 g in each case.

[0062] (1) Target composition: Tb 3 Al 5 O 12 (Example 1-1) m Tb(微粉) =3 / 2×M Tb / M G1-1 ×W×100 / (100-a Tb(微粉) )=36.63(g) m AL =5 / 2×M AL / M G1-1 ×W×100 / (100-a Al )=16.24(g) (Comparative Example 1-1) m' Tb(微粉) =3 / 2×M Tb / M G1-1 ×W=34.14(g) m' AL =5 / 2×M AL / M G1-1 ×W=15.86(g) (M Tb =365.8, M AL =102.0, M G1-1 =803.7, a Tb(微粉) = 6.8, a Al =2.2)

[0063] (2) Target composition: Y 3 Al 5 O 12 (Example 1-2) m Y(微粉) =3 / 2×M Y / M G1-2 ×W×100 / (100-a Y(微粉) )=31.91(g) m AL =5 / 2×M AL / M G1-2 ×W×100 / (100-a Al )=21.96(g) (Comparative Example 1-2) m' Y(微粉) =3 / 2×M Y / M G1-2 ×W=28.53(g) m' AL =5 / 2×M AL / MG1-2 ×W=21.48(g) (M Y =225.8, M AL =102.0, M G1-2 =593.6, a Y(微粉) = 10.6, a Al =2.2)

[0064] (3) Target composition: (Tb 0.8 Y 0.2 ) 3 Al 5 O 12 (Examples 1-3) m Tb(微粉) =3 / 2×0.8×M Tb / M G1-3 ×W×100 / (100-a Tb(微粉) )=30.92(g) m Y(微粉) =3 / 2×0.2×M Y / M G1-3 ×W×100 / (100-a Y(微粉) )=4.97(g) m AL =5 / 2×M AL / M G1-3 ×W×100 / (100-a Al )=17.12(g) (Comparative Example 1-3) m' Tb(微粉) =3 / 2×0.8×M Tb / M G1-3 ×W=28.81(g) m' Y(微粉) =3 / 2×0.2×M Y / M G1-3 ×W=4.45(g) m' AL =5 / 2×M AL / M G1-3 ×W=16.74(g) (M Tb =365.8, M Y =225.8, M AL =102.0, M G1-3 =761.7, a Tb(微粉) = 6.8, a Y(微粉) = 10.6, a Al =2.2)

[0065] (4) Target composition: (Tb 0.6 Y 0.4 ) 3 Al 5 O 12 (Examples 1 to 4) m Tb(微粉) =3 / 2×0.6×M Tb / M G1-4 ×W×100 / (100-a Tb(微粉) )=24.54(g) m Y(微粉) =3 / 2×0.4×M Y / M G1-4 ×W×100 / (100-a Y(微粉) )=10.53(g) m AL =5 / 2×M AL / M G1-4 ×W×100 / (100-a Al )=18.11(g) (Comparative Examples 1-4) m' Tb(微粉) =3 / 2×0.6×M Tb / M G1-4 ×W=22.87(g) m' Y(微粉) =3 / 2×0.4×M Y / M G1-4 ×W=9.41(g) m' AL =5 / 2×M AL / M G1-4 ×W=17.72(g) (M Tb =365.8, M Y =225.8, M AL =102.0, M G1-4 =719.7, a Tb(微粉) = 6.8, a Y(微粉) = 10.6, a Al =2.2)

[0066] (5) Target composition: (Tb 0.6 Y 0.38 Sc 0.02 ) 3 (Al 0.998 Sc 0.002 ) 5 O 12 (Examples 1 - 5) m Tb(微粉) = 3 / 2 × 0.6 × M Tb / M G1-5 × W × 100 / (100 - a Tb(微粉) ) = 25.08 (g) m Y(微粉) = 3 / 2 × 0.38 × M Y / M G1-5 × W × 100 / (100 - a Y(微粉) ) = 10.22 (g) m AL = 5 / 2 × 0.998 × M AL / M G1-5 × W × 100 / (100 - a Al ) = 18.47 (g) m Sc =(3 × 0.02 / 2 + 5 × 0.002 / 2)(M Sc / M G1-5 ) × W × 100 / (100 - a Sc ) = 0.35 (g) (Comparative Examples 1 - 5) m’ Tb(微粉) = 3 / 2 × 0.6 × M Tb / M G1-5 × W = 23.38 (g) m’ Y(微粉) = 3 / 2 × 0.38 × M Y / M G1-5 × W = 9.14 (g) m’ AL = 5 / 2 × 0.998 × M AL / M G1-5 × W = 17.99 (g) m’ Sc =(3 × 0.02 / 2 + 5 × 0.002 / 2)(M Sc / M G1-5 ) × W = 0.34 (g) (M Tb = 365.8, M Y = 225.8, M AL = 102.0, M Sc = 137.9, M G1-5 = 704.2, a Tb(微粉) = 6.8, a Y(微粉) = 10.6, a Al = 2.2, a Sc = 1.4)

[0067] (6) Target composition: (Y 0.999 Ce 0.001 ) 3 Al 5 O 12 (Examples 1 to 6) m Y(微粉) =3 / 2×0.999×M Y / M G1-6 ×W×100 / (100-a Y(微粉) )=31.87(g) m Ce =3 / 2×0.001×M Ce / M G1-6 ×W×100 / (100-a Ce )=0.04(g) m AL =5 / 2×M AL / M G1-6 ×W×100 / (100-a Al )=21.95(g) (Comparative Examples 1-6) m' Y(微粉) =3 / 2×0.999×M Y / M G1-6 ×W=28.49(g) m' Ce =3 / 2×0.001×M Ce / M G1-6 ×W=0.04(g) m' AL =5 / 2×M AL / M G1-6 ×W=21.47(g) (M Y =225.8, M Ce =328.2, M AL =102.0, M G1-6 =593.8, a Y(微粉) = 10.6, a Ce = 5.9, a Al =2.2)

[0068] (7) Target composition: Lu 3 Al 5 O 12 (Examples 1 to 7) m Lu =3 / 2×M Lu / MG1-7 ×W×100 / (100-a Lu )=36.31(g) m AL =5 / 2×M AL / M G1-7 ×W×100 / (100-a Al )=15.30(g) (Comparative Examples 1-7) m' Lu =3 / 2×M Lu / M G1-7 ×W=35.04(g) m' AL =5 / 2×M AL / M G1-7 ×W=14.97(g) (M Lu =398.0, M AL =102.0, M G1-7 =851.9, a Lu = 3.5, a Al =2.2)

[0069] (8) Target composition: Dy 3 Al 5 O 12 (Examples 1 to 8) m Dy =3 / 2×M Dy / M G1-8 ×W×100 / (100-a Dy )=35.45(g) m AL =5 / 2×M AL / M G1-8 ×W×100 / (100-a Al )=16.01(g) (Comparative Examples 1-8) m' Dy =3 / 2×M Dy / M G1-8 ×W=34.35(g) m' AL =5 / 2×M AL / M G1-8 ×W=15.66(g) (M Dy =373.0, M AL =102.0, M G1-8 =814.4, a Dy = 3.1, aAl =2.2)

[0070] (9) Target composition: Tb 3.014 Al 4.986 O 12 (Reference example 1) m Tb(微粉) =3.014 / 2×M Tb / M G1-9 ×W=34.22(g) m AL =4.986 / 2×M AL / M G1-9 ×W=15.79(g) (M Tb =365.8, M AL =102.0, M G1-9 =805.4)

[0071] For each target composition, the starting material was weighed out in the amount determined as above. A precision balance capable of measuring to four decimal places was used for the weighing. The weighed starting material (oxide powder) was placed in a ball mill container. Then, ethanol was added so that the concentration of the oxide powder was 30 mass%, and 0.01 mass% of polyethylene glycol was added as a dispersant, and TEOS (Kishida Chemical Co., Ltd.) was added as a sintering aid so that the concentration was 100 ppm in terms of Si. Next, alumina balls with a diameter of 2 mm were placed in the ball mill container, which was then set on a rotating table, and ball mill mixing was performed for 20 hours. A polyvinyl alcohol binder (manufactured by Kuraray Co., Ltd.) was added as a binder to the obtained slurry in an amount of 1.5 mass % based on the powder amount, and the mixture was further mixed in a ball mill for 4 hours. Finally, the slurry was separated from the alumina balls, and the raw material was granulated by spray drying.

[0072] (molding process) The granules obtained in the previous process were filled into a cylindrical mold and molded into a specified shape by dry uniaxial press molding. The molded body was a cylinder with a diameter of 8 mm and a length of 40 mm. The uniaxial press molded body was then subjected to CIP treatment at a pressure of 198 MPa, and the relative density of the molded body was set to 60%. (Degreasing process) The obtained CIP molded body was degreased at 270℃ for 3 hours. The removal of organic matter was confirmed and the amount of oxygen absorbed by degreasing was measured by the above-mentioned TG analysis. The decomposition of organic matter was judged by the weight loss up to 400℃, and the amount of oxygen absorbed was compared by the weight increase around 400℃. (Sintering process) The sintering process was carried out in two stages: preliminary sintering and HIP treatment. First, the degreased compact was placed in a vacuum sintering furnace and sintered at a vacuum of 1×10 -4 The pre-sintering process was carried out under conditions of 100 Pa, a heating rate of 100°C / h, and a holding time of 1600°C for 2 hours. The density of all samples after pre-sintering was 93% or higher. Next, in order to make the samples transparent, the pre-sintered samples were subjected to HIP processing at 1600°C for 3 hours in an Ar atmosphere at a pressure of 198 MPa. Although the samples after HIP were transparent, blackening due to oxygen defects was visible, so an oxidation annealing process was carried out in air at 1450°C for 30 hours. All samples after oxidation annealing were colorless and transparent. (polishing / processing process) The annealed HIP sintered sample was cylindrically ground to an outer diameter of 5 mm, and then optically polished to a length of 20 mm. The processing conditions were adjusted so that the polished surface accuracy was λ / 8 (λ=633 nm).

[0073] The transparent ceramic samples obtained as described above were evaluated as follows. (Transmittance measurement) The transparency of the optically polished transparent ceramic sample was measured with reference to JIS K7136:2000. That is, an entrance opening and an exit opening through which light passes are provided in an integrating sphere, and a sample (transparent ceramic sample) is placed at the entrance opening. By attaching a reflector to the exit opening, it becomes possible to detect all the light emitted from the sample with the integrating sphere, and the total light transmittance is measured from the ratio of the intensity of the detected exit light to the intensity of the light incident on the sample. The device used was a spectrophotometer (V-670) manufactured by JASCO Corporation, and the measurement was performed using the attached integrating sphere. At that time, a pinhole was provided so that the spot diameter of the irradiated light was 3 mm. The measurement wavelength was fixed at 1064 nm. The above results are shown in Table 2.

[0074] [Table 2]

[0075] As a result, as in Examples 1-1 to 1-8, when the starting materials were weighed by the mass used corrected by the mass reduction rate (a(%)) at 1100°C, all of them were highly transparent. On the other hand, as in Comparative Examples 1-1 to 1-8, when the starting materials were weighed by the mass used calculated as in the conventional manner without correcting by the mass reduction rate (a(%)) at 1100°C, a decrease in transmittance due to deviation in the ceramic composition was observed. It should be noted that, as in Reference Example 1, it is possible to obtain highly transparent ceramics by shifting the target composition from the ideal ratio even without correcting by the mass reduction rate (a(%)) at 1100°C for the starting materials. These results suggest that ceramics with a composition different from the target composition are produced due to the influence of moisture adsorbed on the oxide powder of the starting materials. It should be noted that "highly transparent" here refers to a transmittance of 82% or more. In addition, "heterogeneous phase" in the remarks column means that a heterogeneous phase was observed by observation with an optical microscope at a magnification of 100 times (hereinafter the same).

[0076] [Example 2] In Example 1-1 and Comparative Example 1-1, the starting material Tb oxide powder was replaced with Tb 4 O 7 The mass of the coarse powder used was calculated as follows, and otherwise the transparent ceramic samples were produced in the same manner as in Example 1-1 and Comparative Example 1-1. In Reference Example 1, the starting material Tb oxide powder was replaced with Tb 4 O 7 A transparent ceramic sample was produced in the same manner as in Reference Example 1, except for using (coarse powder). The results are shown in Table 3. ·Target composition: Tb 3 Al 5 O 12 Example 2 m Tb(粗粉) =3 / 2×M Tb / M G2 ×W×100 / (100-a Tb(粗粉) )=35.12(g) m AL =5 / 2×M AL / M G2 ×W×100 / (100-a Al )=16.22(g) Comparative Example 2 m' Tb(粗粉) =3 / 2×M Tb / M G2 ×W=34.14(g) m' AL =5 / 2×M AL / M G2 ×W=15.86(g) (M Tb =365.8, M AL =102.0, M G2 =803.7, a Tb(粗) = 2.8, a Al =2.2) ·Target composition: Tb 3.014 Al 4.986 O 12 (Reference example 2) m Tb(粗粉) =3.014 / 2×M Tb / M G1-9 ×W=34.22(g) m AL =4.986 / 2×M AL / MG1-9 ×W=15.79(g) (M Tb =365.8, M AL =102.0, M G1-9 =805.4)

[0077] [Table 3]

[0078] As a result of the above, high transparency was achieved in Example 2, whereas the transmittance was low in Comparative Example 2. Moreover, in Reference Example 2, the transmittance was poor, despite the target composition (weighing conditions) that achieved high transparency in Reference Example 1. It is believed that the difference between Reference Example 1 and Reference Example 2 was due to differences in the amount of adsorbed moisture in the oxide powder, which is the starting material. As described above, according to the manufacturing method of the present invention, it is possible to produce highly transparent garnet-type ceramics with good reproducibility even if the type or lot of the starting oxide powder is changed.

[0079] [Example 3] In the above Examples 1-3 and 1-4 and Comparative Examples 1-3 and 1-4, the combination of Tb oxide powder and Y oxide powder was Tb 4 O 7 (Fine powder)-Y 2 O 3 (coarse powder), Tb 4 O 7 (coarse powder)-Y 2 O 3 (fine powder) and the mass used was calculated as follows, but otherwise transparent ceramic samples were produced in the same manner as in Examples 1-3 and 1-4 and Comparative Examples 1-3 and 1-4. (1) Target composition: (Tb 0.8 Y 0.2 ) 3 Al 5 O 12 (Example 3-1) m Tb(微粉) =3 / 2×0.8×M Tb / M G3(1) ×W×100 / (100-a Tb(微粉))=30.92(g) m Y(粗粉) =3 / 2×0.2×M Y / M G3(1) ×W×100 / (100-a Y(粗粉) )=4.60(g) m AL =5 / 2×M AL / M G3(1) ×W×100 / (100-a Al )=17.12(g) (Comparative Example 3-1) m' Tb(微粉) =3 / 2×0.8×M Tb / M G3(1) ×W=28.81(g) m' Y(粗粉) =3 / 2×0.2×M Y / M G3(1) ×W=4.45(g) m' AL =5 / 2×M AL / M G3(1) ×W=16.74(g) (Example 3-2) m Tb(粗粉) =3 / 2×0.8×M Tb / M G3(1) ×W×100 / (100-a Tb(粗粉) )=29.64(g) m Y(微粉) =3 / 2×0.2×M Y / M G3(1) ×W×100 / (100-a Y(微粉) )=4.97(g) m AL =5 / 2×M AL / M G3(1) ×W×100 / (100-a Al )=17.12(g) (Comparative Example 3-2) m' Tb(粗粉) =3 / 2×0.8×M Tb / M G3(1) ×W=28.81(g) m' Y(微粉) =3 / 2×0.2×M Y / M G3(1) ×W=4.45(g) m' AL =5 / 2×M AL / MG3(1) ×W=16.74(g) (M Tb =365.8, M Y =225.8, M AL =102.0, M G3(1) =761.7, a Tb(微粉) = 6.8, a Tb(粗粉) = 2.8, a Y(微粉) = 10.6, a Y(粗粉) = 3.4, a Al =2.2)

[0080] (2) Target composition: (Tb 0.6 Y 0.4 ) 3 Al 5 O 12 (Example 3-3) m Tb(微粉) =3 / 2×0.6×M Tb / M G3(2) ×W×100 / (100-a Tb(微粉) )=24.54(g) m Y(粗粉) =3 / 2×0.4×M Y / M G3(2) ×W×100 / (100-a Y(粗粉) )=9.74(g) m AL =5 / 2×M AL / M G3(2) ×W×100 / (100-a Al )=18.11(g) (Comparative Example 3-3) m' Tb(微粉) =3 / 2×0.6×M Tb / M G3(2) ×W=22.87(g) m' Y(粗粉) =3 / 2×0.4×M Y / M G3(2) ×W=9.41(g) m' AL =5 / 2×M AL / M G3(2) ×W=17.72(g) (Examples 3-4) m Tb(粗粉) =3 / 2×0.6×M Tb / M G3(2) ×W×100 / (100-aTb(粗粉) )=23.53(g) m Y(微粉) =3 / 2×0.4×M Y / M G3(2) ×W×100 / (100-a Y(微粉) )=10.53(g) m AL =5 / 2×M AL / M G3(2) ×W×100 / (100-a Al )=18.11g) (Comparative Example 3-4) m' Tb(粗粉) =3 / 2×0.6×M Tb / M G3(2) ×W=22.87(g) m' Y(微粉) =3 / 2×0.4×M Y / M G3(2) ×W=9.41(g) m' AL =5 / 2×M AL / M G3(2) ×W=17.72(g) (M Tb =365.8, M Y =225.8, M AL =102.0, M G3(2) =719.7, a Tb(微粉) = 6.8, a Tb(粗粉) = 2.8, a Y(微粉) = 10.6, a Y(粗粉) = 3.4, a Al =2.2)

[0081] For the transparent ceramic sample obtained as described above, the transmittance was measured, and the Verdet constant was also measured on the assumption that an isolator was installed as described below. (Verde constant) Garnet-type transparent ceramics containing Tb have magneto-optical effects and can be used as materials for isolators. To investigate whether the obtained transparent ceramics can be used as isolators, the Verdet constant was measured. As shown in Figure 1, each ceramic sample was inserted into the center of a neodymium-iron-boron magnet with an outer diameter of 32 mm, an inner diameter of 6 mm, and a length of 40 mm, and polarizers were inserted at both ends. Then, a high-power laser beam with a wavelength of 1064 nm was irradiated from both ends using a high-power laser (beam diameter 1.6 mm) manufactured by IPG Photonics Japan Co., Ltd., to determine the Faraday rotation angle θ. The Faraday rotation angle θ was defined as the angle at which the maximum transmittance was observed when the polarizer on the output side was rotated. The Verdet constant was calculated based on the following formula. The magnitude of the magnetic field (H) applied to the sample was calculated by simulation using the dimensions of the measurement system, the residual magnetic flux density (Br), and the coercive force (Hc). θ=V×H×L (In the formula, θ is the Faraday rotation angle (Rad), V is the Verdet constant (Rad / (T m)), H is the magnitude of the magnetic field (T), and L is the length of the Faraday rotator (0.020 m in this case).) The above results are shown below together with the results of the Verdet constants measured for the transparent ceramic samples of Examples 1-1, 1-3, 1-4, 1-5, and 2 and Comparative Examples 1-1, 1-3, 1-4, 1-5, and 2.

[0082] [Table 4]

[0083] [Table 5]

[0084] In all cases, the Verdet constants of the examples and the comparative examples were not the same. This is thought to be because the comparative examples did not include correction based on the mass reduction rate (a(%)) of the starting material at 1100°C, which caused the balance between Tb and other elements to be lost from the target composition, resulting in a difference from the Verdet constants of the examples. In other words, in the conventional manufacturing method, when the target composition is fixed to an ideal ratio, it is expected that the Verdet constant will vary due to the influence of the type (specific surface area, etc.) of the Tb oxide powder and other oxide powders in the starting material. If the Verdet constant varies, it is not preferable because it may affect the quality of the isolator and may deteriorate the extinction ratio of the return light. As described above, the present invention is effective not only in making transparent ceramics highly transparent, but also in ensuring the performance of magneto-optical elements.

[0085] Although the present invention has been described above using the above-mentioned embodiment, the present invention is not limited to this embodiment, and can be modified within the scope of what a person skilled in the art can imagine, such as other embodiments, additions, modifications, deletions, etc., and any aspect is within the scope of the present invention as long as it achieves the effects of the present invention. [Explanation of symbols]

[0086] 100 Optical isolator 110 Faraday Rotator 120 Polarizer 130 Analyzer 140 Magnet

Claims

1. Using as starting materials at least one oxide powder selected from Sc, Y and lanthanoid elements and one oxide powder selected from Group 13 elements, a powder represented by the following formula (1) was prepared. (A 1 1-x-y A 2 x Sc y ) 3 (B 1-z Sc z ) 5 O 12 (1) (In formula (1), A 1 , A 2 are elements different from each other selected from Y and the lanthanoid elements, B is one selected from the Group 13 elements, 0≦x≦0.4, 0≦y<0.08, 0≦z<0.16, and when z=0, y=0, and when z>0, y>0. A method for producing a rare earth garnet-type transparent ceramic, which is a sintered body of a complex oxide represented by the following formula: A 1 and A 2 are different elements selected from Tb, Y, Ce, Lu and Dy, B is Al, As the starting material, powders of oxides of different elements selected from Tb, Y, Ce, Lu and Dy, each having a purity of 99.9% by mass or more, are used in an amount of m calculated by the following formulas (2-1) and (2-2): A1 , m A2 The mass m of the aluminum oxide powder having a purity of 99.9% by mass or more is calculated by the following formula (2-3): B The mass m of scandium oxide powder having a purity of 99.9% by mass or more is calculated by the following formula (2-4): Sc The method for producing rare earth garnet-type transparent ceramics is as follows: m A1 =3 / 2×(1-x-y)M A1 / M G ×W×100 / (100-a A1 ) (2-1) m A2 =3 / 2×xM A2 / M G ×W×100 / (100-a A2 ) (2-2) m B =5 / 2×(1-z)M B / M G ×W×100 / (100-a B ) (2-3) m Sc =(3y / 2+5z / 2)(M Sc / M G )×W×100 / (100-a Sc ) (2-4) (In the formula, M A1 , M. A2 are the molar masses (g / mol) of oxides of different elements selected from Tb, Y, Ce, Lu and Dy, and M B is the molar mass of the oxide of Al (g / mol), M Sc is the molar mass of scandium oxide (g / mol), M G is the molar mass (g / mol) of the composite oxide represented by formula (1), W is the planned total mass (g) of the starting materials, A1 , a A2 is the mass reduction rate (%) when the starting material oxide powders of different elements selected from Tb, Y, Ce, Lu and Dy are heated in an inert gas atmosphere from room temperature (20±10° C.) to 1100° C., B is the mass reduction rate (%) when the starting Al oxide powder is heated from room temperature (20±10° C.) to 1100° C. in an inert gas atmosphere, and a Sc is the mass reduction rate (%) when the starting scandium oxide powder is heated from room temperature (20±10°C) to 1100°C in an inert gas atmosphere. x, y, and z are the same as above.

2. The sintered body contains SiO 2 2. The method for producing a rare earth garnet-type transparent ceramic according to claim 1, wherein the rare earth garnet-type transparent ceramic contains more than 0 mass % and 0.1 mass % or less of

3. A in the above formula (1) 1 3. The method for producing a rare earth garnet-type transparent ceramic according to claim 1, wherein xy is Tb and 0.6≦1−x−y≦1.

4. The method for producing a rare earth garnet-type transparent ceramic according to any one of claims 1 to 3, wherein the starting materials are molded, and then the obtained molded body is degreased and sintered to obtain a sintered body of the composite oxide.

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