JP2023109324A - Method of producing paramagnetic garnet type transparent ceramic - Google Patents

Abstract

To provide a method of producing paramagnetic garnet type transparent ceramic, i.e., a sintered body of a paramagnetic garnet type oxide containing Tb and Y, which ceramic is highly transparent, is of extremely high and stable production reproducibility, and is truly practically usable.SOLUTION: The method of producing paramagnetic garnet type transparent ceramic constituted of a sintered body of a composite oxide of a prescribed composition including Tb, Y, Sc and Al, by wet-blending terbium oxide powder, yttrium oxide powder, scandium oxide powder and aluminum oxide powder as starting materials, and silicon dioxide as a sintering aid to prepare slurry, molding the slurry and sintering the molding, is characterized in that the mean particle diameters of terbium oxide powder and yttrium oxide powder are each 3 μm or more, and the mean particle diameters of scandium oxide powder and aluminum oxide powder are each smaller than 1 μm, the particle size distributions of the terbium oxide powder, yttrium oxide powder, scandium oxide powder and aluminum oxide powder in the slurry each have a single peak, the median diameter (D50 value) in each of the particle diameter distributions is 400 nm or more, and the value of cumulative volume-based 95% mean particle diameter from the smallest value side in the particle size distribution (D95 value), is 2 μm or less.SELECTED DRAWING: Figure 2

Description

TECHNICAL FIELD The present invention relates to a method for producing a paramagnetic garnet-type transparent ceramic, and more particularly, a garnet-type transparent ceramic containing terbium and yttrium suitable for forming a magneto-optical device such as an optical isolator. It relates to a manufacturing method.

In recent years, it has become possible to increase the output of fiber lasers, and the spread of laser processing machines using such fiber lasers is remarkable. By the way, when light from the outside enters a laser light source incorporated in a laser processing machine, the resonance state becomes unstable, and a phenomenon occurs in which the oscillation state is disturbed. In particular, when the oscillated light is reflected by an optical system on the way and returns to the light source, the oscillation state is greatly disturbed. To prevent this, an optical isolator is usually provided on the light exit side of the light source, such as between the laser light source and the optical fiber.

The optical isolator comprises a Faraday rotator, a polarizer arranged on the light incident side of the Faraday rotator, and an analyzer arranged on the light exit side of the Faraday rotator. Also, the Faraday rotator applies a magnetic field parallel to the light traveling direction. At this time, the polarization line segment of the light rotates only in a fixed direction regardless of whether it moves forward or backward in the Faraday rotator. In addition, the Faraday rotator is adjusted to a length such that the polarization line segment of the light is rotated exactly 45 degrees. Here, if the planes of polarization of the polarizer and the analyzer are shifted by 45 degrees in the direction of rotation of the advancing light, the polarization of the advancing light matches the position of the polarizer and that of the analyzer, and is thus transmitted. On the other hand, the polarized wave of the backward traveling light is rotated 45 degrees in the direction opposite to the shift angle direction of the plane of polarization of the polarizer which is shifted by 45 degrees from the position of the analyzer. Then, the plane of polarization of the return light at the position of the polarizer deviates from the plane of polarization of the polarizer by 45 degrees - (-45 degrees) = 90 degrees, and cannot pass through the polarizer. In this way, it functions as an optical isolator that transmits and emits advancing light and blocks backward returning light.

TGG crystal (Tb ₃ Ga ₅ O ₁₂ ) and TSAG crystal ((Tb _(3-x) Sc _x )Sc ₂ Al ₃ O ₁₂ ) are conventionally known materials for use as the Faraday rotator constituting the optical isolator. (JP-A-2011-213552 (Patent Document 1), JP-A-2002-293693 (Patent Document 2)). TGG crystals are now widely installed for standard fiber laser devices. On the other hand, the Verdet constant of TSAG crystal is said to be about 1.3 times that of TGG crystal. Recruitment has not progressed from the aspect of

In addition to the above, TAG crystal (Tb ₃ Al ₅ O ₁₂ ) has long been known as a Faraday rotator having a Verdet constant larger than that of TSAG. However, since the TAG crystal is a decomposition melting type crystal, there is a limitation that the perovskite phase is first generated at the solid-liquid interface, and then the TAG phase is generated. In other words, the garnet phase and the perovskite phase of the TAG crystal can only be grown in a state where they are always mixed, and the TAG crystal growth of good quality and large size has not been realized.

In Japanese Patent No. 3642063 (Patent Document 3) and Japanese Patent No. 4107292 (Patent Document 4), as means for suppressing this mixed crystal, a polycrystalline raw material rod for FZ growth or a seed crystal is made porous. Therefore, a method has been proposed in which the perovskite phase, which is the primary phase, is preferentially precipitated in the porous medium. However, in reality, as the melting position moves, the position where the perovskite phase is likely to precipitate also moves. Complete suppression was essentially impossible.

Under these constraints, a dense ceramic sintered body having a composition of (Tb _x Y _1-x ) ₃ Al ₅ O ₁₂ (x = 0.5 to 1.0) has recently been developed as an existing TGG crystal. (existing 35 dB is improved to 39.5 dB or more) and insertion loss can be reduced (existing 0.05 dB is improved to 0.01 to 0.05 dB). Yan Lin Aung, Akio Ikesue, Development of optical grade ( _{TbxY1 -x} ) _{3Al5O12 ceramics} as Faraday rotator material, J.Am.Ceram.Soc., (2017), 1 00(9), _4081- 4087 (Non-Patent Document 1)). Since the material disclosed in Non-Patent Document 1 is first of all ceramics, there is no precipitation of the perovskite heterogeneous phase, which has been a problem with TGG crystals. It is a material that has made it possible to reduce the loss and is a material from which a very high-quality garnet-type Faraday rotator can be obtained.

Furthermore, Japanese Patent Application Laid-Open No. 2019-199386 (Patent Document 5) describes (Tb _1-xy Y _x Sc _y ) ₃ (Al _1-z Sc _z ) ₅ O ₁₂ (where 0.05≦x< 0.45, 0<y<0.1, 0.5<1-xy<0.95, 0.004<z<0.2). It is This material has a composition similar to that of Non-Patent Document 1, but differs in that Sc is significantly added. This material has an extinction ratio of 40 dB or more, which is even more improved than that of Non-Patent Document 1. Even when irradiated with a 100 W laser, the amount of change in the focal position due to the thermal lens is small. , It is said that it is a truly practical paramagnetic garnet-type transparent ceramic that is easy to scale up because it is made of ceramic.

By the way, Japanese Patent No. 6119528 (Patent Document 6) discloses a method for producing a transparent sesquioxide sintered body, in which the particle size distribution of oxide particles of a rare earth element (the particles aggregate to form secondary particles If it is, it is the particle size distribution of this secondary particle.) In the raw material powder whose cumulative particle diameter (D2.5 value) of 2.5% by volume from the minimum value side is 180 nm or more and 2000 nm or less, further D2.5 180 nm or more and 280 nm or less, and the D50 value, which is the median diameter, is 950 nm or less. It is possible to stably provide a transparent sintered body with

JP 2011-213552 A JP-A-2002-293693 Japanese Patent No. 3642063 Japanese Patent No. 4107292 JP 2019-199386 A Japanese Patent No. 6119528

Yan Lin Aung, Akio Ikesue, Development of optical grade (TbxY1-x)3Al5O12 ceramics as Faraday rotator material, J.Am.Ceram.Soc., (2017), 100(9), 40 81-4087

However, when the inventors of the present invention actually repeated experiments under the conditions of Non-Patent Document 1 and Patent Document 5, the reproducibility was considerably poor, and it was difficult to obtain a high-quality ceramic sintered body with a smaller insertion loss than the TGG crystal. It was confirmed that

In addition, the transparent sesquioxide sintered body in Patent Document 6 differs from the paramagnetic garnet-type transparent ceramics sintered body in composition and crystal structure. , suggesting that it is important to control the particle size and particle size distribution of the raw material powder used. However, no information has been disclosed about the particle size and particle size distribution of the raw material powder for finishing the paramagnetic garnet-type transparent ceramics sintered body into a highly transparent sintered body stably with good reproducibility.

The present invention has been made in view of the above circumstances, and is a sintered body of a paramagnetic garnet-type oxide containing terbium and yttrium, which has extremely high transparency, extremely high reproducibility in production, and is stable. An object of the present invention is to provide a truly practical method for producing paramagnetic garnet-type transparent ceramics.

In order to achieve the above object, the present inventors have made intensive studies on a method for stably producing a sintered body of a paramagnetic garnet-type oxide containing terbium and yttrium based on the knowledge of the above known examples. I came up with the invention.

That is, the present invention provides the following method for producing paramagnetic garnet-type transparent ceramics.
1.
Terbium oxide powder, yttrium oxide powder, scandium oxide powder, and aluminum oxide powder as starting materials and _SiO2 raw material as a sintering aid are wet-mixed to form a slurry, and after molding using the slurry, the obtained The molded body is degreased and sintered, and the following formula (1)

₍ Tb1 _{-xyYxScy ) 3 (} Al1 _{-zScz ) 5O12} (1)
(Wherein, 0.05 ≤ x ≤ 0.4, 0 ≤ y < 0.08, 0.52 < 1-xy < 0.95, 0 ≤ z < 0.2, 0.001 < y + z < 0.2.)

Manufacture of paramagnetic garnet _- type transparent ceramics to obtain paramagnetic garnet-type transparent ceramics which is a sintered body of a composite oxide represented by in the method
The average particle size of the terbium oxide powder and the yttrium oxide powder as the starting materials is 3 μm or more, and the average particle size of the scandium oxide powder and the aluminum oxide powder as the starting materials is less than 1 μm, and the terbium oxide in the slurry The particle size distribution of the powder, the yttrium oxide powder, the scandium oxide powder, and the aluminum oxide powder has a single peak, the D50 value, which is the median diameter of the particle size distribution, is 400 nm or more, and the minimum value side of the particle size distribution A method for producing paramagnetic garnet-type transparent ceramics, characterized in that the D95 value, which is the cumulative value of 95% by volume, is 2 μm or less.
2.
2. The method for producing paramagnetic garnet-type transparent ceramics according to 1, wherein the wet mixing is by a ball mill or a bead mill.
3.
3. The method for producing paramagnetic garnet-type transparent ceramics according to 2, wherein the mixing time in the ball mill or bead mill is 1 hour or more and 15 hours or less.
4.
3. The method for producing paramagnetic garnet-type transparent ceramics according to any one of 1 to 3, wherein the dispersion medium for wet mixing is a lower alcohol having 1 to 3 carbon atoms.
5.
5. The method for producing paramagnetic garnet-type transparent ceramics according to any one of 1 to 4, wherein the particle size distribution is for slurry containing no binder.
6.
6. The paramagnetic garnet-type transparent material according to any one of 1 to 5, wherein when the slurry is allowed to stand after being wet-mixed, the terbium oxide powder and/or yttrium oxide powder precipitate immediately after that to form a deposited layer. Manufacturing method of ceramics.
7.
7. The method for producing paramagnetic garnet-type transparent ceramics according to any one of 1 to 6, wherein the slurry is spray-dried to obtain a granular raw material, and the granular raw material is used for molding.

According to the present invention, a paramagnetic garnet-type oxide sintered body containing terbium and yttrium can be stably and highly transparently finished with good reproducibility. Practical paramagnetic garnet-type oxide transparent ceramics can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a cross-sectional schematic diagram which shows the structural example of the optical isolator using the paramagnetic garnet-type transparent ceramics manufactured by this invention as a Faraday rotator. Oxide raw material No. in the examples. 3 is a diagram showing the particle size distribution for each mixing time of the slurry using No. 3. FIG. Oxide raw material No. in the examples. 6 is a diagram showing the particle size distribution for each mixing time of the slurry using No. 6. FIG.

The configuration of the method for producing paramagnetic garnet-type transparent ceramics according to the present invention will be described below.
In the method for producing the paramagnetic garnet-type transparent ceramics of the present invention, terbium oxide powder, yttrium oxide powder, scandium oxide powder and aluminum oxide powder as starting materials and _SiO2 raw material as a sintering aid are wet-mixed. After forming a slurry using the slurry, the obtained formed body is degreased and sintered to obtain the following formula (1)

₍ Tb1 _{-xyYxScy ) 3 (} Al1 _{-zScz ) 5O12} (1)
(Wherein, 0.05 ≤ x ≤ 0.4, 0 ≤ y < 0.08, 0.52 < 1-xy < 0.95, 0 ≤ z < 0.2, 0.001 < y + z < 0.2.)

Manufacture of paramagnetic garnet _- type transparent ceramics to obtain paramagnetic garnet-type transparent ceramics which is a sintered body of a composite oxide represented by in the method
(a) the average particle size of each of the terbium oxide powder and the yttrium oxide powder as the starting materials is 3 μm or more, and the average particle size of each of the scandium oxide powder and the aluminum oxide powder as the starting materials is less than 1 μm,
(b) the particle size distribution of the terbium oxide powder, the yttrium oxide powder, the scandium oxide powder, and the aluminum oxide powder in the slurry has a single peak, and the D50 value, which is the median diameter of the particle size distribution, is 400 nm or more; The D95 value, which is the cumulative 95 volume % value from the minimum value side of the particle size distribution, is 2 μm or less.

(transparent ceramics)
The transparent ceramic produced in the present invention is a sintered body of a paramagnetic garnet-type composite oxide containing Tb and Y, and is a transparent sintered body of the composite oxide represented by the above composition formula (1). is. When a paramagnetic garnet-type transparent ceramic having a composition within the range represented by the above formula (1) is produced, it has extremely small optical scattering, minimal distortion and absorption, and has a sufficient Verdet constant as a Faraday rotator. can do.

Specifically, terbium (Tb) is added in the concentration range represented by formula (1) to ensure a sufficient Verdet constant, and yttrium (Y) is added in the concentration range represented by formula (1). By doing so, it is possible to secure suppression of heterogeneous phases and minimization of internal strain. Further, by adding scandium (Sc) within the concentration range represented by the formula (1), the heterogeneous phase is completely eliminated. Furthermore, by adding aluminum (Al) within the concentration range represented by formula (1), a sufficient Verdet constant is ensured and a relatively high thermal conductivity is imparted.

The numerical ranges of x, y, and z in formula (1) are detailed below.
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. With x in this range, the perovskite heterophase can be reduced to a level that is undetectable by X-ray diffraction (XRD) analysis.

If x is less than 0.05, the effect of replacing part of terbium with yttrium cannot be obtained, and the conditions are substantially the same as those for producing TAG. It is not preferable because it becomes difficult to Moreover, when x is larger than 0.4, the Verdet constant at a wavelength of 1064 nm becomes less than 32 rad/(T·m), which is not preferable. Furthermore, if the relative concentration of terbium is excessively diluted, the total length required to rotate the laser beam with a wavelength of 1064 nm by 45 degrees becomes longer than 25 mm, which is not preferable because the manufacturing becomes difficult.

In formula (1), the range of y is 0≦y<0.08, preferably 0.001<y<0.004, more preferably 0.002<y<0.004. When y is in this range, the perovskite heterogeneous phase can be reduced to a level that is not detected by X-ray diffraction (XRD) analysis, which is preferable. Furthermore, it is preferable because it can prevent an excessive decrease in thermal conductivity due to homogeneity of the sintered body and grain boundary scattering.

When y is 0.08 or more, while the effect of suppressing the precipitation of the perovskite-type heterogeneous phase or the alumina heterophase is saturated and does not change, sintering unevenness and sintering distortion due to the sintering suppressing effect of scandium are excessively effective. Residual or residual grain boundary scattering occurs, resulting in a local decrease in extinction ratio and a decrease in the average value of thermal conductivity, which is not preferable.

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

In formula (1), the range of z is 0≦z<0.2, preferably 0.001<z<0.004, more preferably 0.02≦z<0.004. When z is within this range, the perovskite heterogeneous phase can be reduced to a level that is not detected by X-ray diffraction (XRD) analysis, which is preferable. Furthermore, it is preferable because it can prevent an excessive decrease in thermal conductivity due to homogeneity of the sintered body and grain boundary scattering.

When z is 0.2 or more, while the effect of suppressing the precipitation of the perovskite type heterophase or the alumina heterophase is saturated and does not change, the sintering suppression effect of scandium is excessively effective, resulting in uneven sintering and sintering distortion. Residual or residual grain boundary scattering occurs, resulting in a local decrease in extinction ratio and a decrease in the average value of thermal conductivity, which is not preferable.

In formula (1), the range of y+z is 0.001<y+z<0.2, more preferably 0.002<y+z<0.005, and still more preferably 0.003<z<0.005. When y+z is in this range, the perovskite heterogeneous phase can be reduced to a level not detected by X-ray diffraction (XRD) analysis, which is preferable. Furthermore, it is preferable because it can prevent an excessive decrease in thermal conductivity due to homogeneity of the sintered body and grain boundary scattering.

If y+z is 0.001 or less, the risk of precipitation of perovskite type heterophase or alumina heterophase increases, which is not preferable. In addition, when y+z is 0.2 or more, while the effect of suppressing the precipitation of the perovskite-type heterogeneous phase or the alumina heterophase is saturated and does not change, the sintering suppressing effect of scandium is excessively effective, resulting in uneven sintering and sintering distortion. or grain boundary scattering, resulting in a local decrease in the extinction ratio and a decrease in the average value of thermal conductivity.

By the way, the paramagnetic garnet-type transparent ceramics obtained in the present invention contains, as a main component, a component having a composition within the range represented by the formula (1), and as an auxiliary component, 0 SiO ₂ which functions as a sintering aid. .1% by mass as a limit, and contained in a range not more than 1% by mass. When a small amount of SiO ₂ is added as a sintering aid, the precipitation of perovskite-type heterogeneous phases, alumina heterophases, etc. is suppressed, so that the transparency of the paramagnetic garnet-type transparent ceramics is further improved. Furthermore, the SiO ₂ added in a small amount vitrifies during sintering at 1400° C. or higher to bring about a liquid-phase sintering effect, and can promote densification of the garnet-type ceramic sintered body. However, if more than 0.1% by mass of _SiO2 is added, the beam diameter changes when a 100 W laser beam with a wavelength of 1064 nm and a beam diameter of 1.6 mm is incident on a paramagnetic garnet type transparent ceramic with a length (optical path length) of 25 mm. Since the amount exceeds 10%, it is not preferable.

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

Moreover, the paramagnetic garnet-type transparent ceramic obtained in the present invention is composed of the above main component and subcomponents, but may further contain other elements. Other elements include rare earth elements such as lutetium (Lu) and cerium (Ce), and various impurity groups such as sodium (Na), calcium (Ca), magnesium (Mg), phosphorus (P), tungsten (W ), molybdenum (Mo) and the like can be typically exemplified.

The content of other elements is preferably 10 parts by mass or less, more preferably 0.1 parts by mass or less, and 0.001 parts by mass or less when the total amount of Tb and Y is 100 parts by mass. (substantially zero) is particularly preferred.

(starting material)
Terbium, yttrium, scandium, and aluminum oxide powders (that is, terbium oxide powder, yttrium oxide powder, scandium oxide powder, and aluminum oxide powder) are used as starting materials for use in the present invention. These powders are called raw material powders for garnet-type composite oxides. The purity of the raw material powder for garnet-type composite oxide is preferably 99.9% by mass or more, particularly preferably 99.99% by mass or more.

In the present invention, terbium oxide powder, yttrium oxide powder, scandium oxide powder, and aluminum oxide powder as starting materials are precisely weighed so as to obtain the composition of the composite oxide represented by the above formula (1), or they are used as they are. are precisely weighed and mixed to prepare a mixed powder for the production of paramagnetic garnet type transparent ceramics. When each constituent element of paramagnetic garnet-type transparent ceramics (oxide sintered body) containing terbium and yttrium finally synthesized is precisely weighed as individual oxide raw materials and then mixed, coprecipitation etc. It is preferable because the weighing accuracy is remarkably improved compared to mixing by the method.

Various organic additives may be added to the oxide powder raw material used in the present invention for the purpose of stabilizing the quality and improving the yield in the subsequent ceramic manufacturing process. In the present invention, these are also not particularly limited. That is, various dispersants, binders, lubricants, plasticizers, and the like can be suitably used. However, as these organic additives, it is preferable to select high-purity types that do not contain unnecessary metal ions. In addition, the order of addition of each organic additive must be appropriately designed so as not to hinder the control of the properties (particle size distribution, etc.) of the raw material to be produced.

Among the starting materials, the terbium oxide powder and the yttrium oxide powder are selected from coarse powders having an average particle size of 3 μm or more, preferably 3 μm or more and 6 μm or less before mixing. As a result, the specific surface areas of these two oxide powders (terbium oxide powder and yttrium oxide powder) are kept extremely small, thereby minimizing the effects of adsorbed moisture and adsorbed gases, as well as the effects of changes in valence during temperature rise. Since it is suppressed, it is possible to accurately weigh and mix each oxide element so as to obtain a garnet composition, which is preferable. Furthermore, terbium oxide powder is preferable because it suppresses a rapid increase in the bulk density of the powder due to a change in valence during temperature rise.

Among the starting materials, the scandium oxide powder and the aluminum oxide powder are fine powders having an average particle size of less than 1 μm, preferably 200 nm or more and 600 nm or less before mixing. This promotes sinterability when sintering the mixed raw material, so that even if coarse powders of terbium oxide powder and yttrium oxide powder are used, the sinterability of the mixed raw material as a whole is maintained.

The average particle size here means the average value of the primary particle size in a state where the oxide raw material powder of the starting material is not agglomerated. It can be determined by measuring the particle size of individual (preferably 20 or more) primary particles by image analysis and calculating the average value.

(wet mixing)
The terbium oxide powder, yttrium oxide powder, scandium oxide powder and aluminum oxide powder as the precisely weighed starting raw materials and the SiO ₂ raw material as the sintering aid are wet-mixed to form a slurry. The wet mixing is a process of dispersing and mixing the starting material and the SiO ₂ material as a sintering aid in a dispersion medium, preferably using a ball mill or bead mill.

The SiO ₂ raw material that serves as the sintering aid is preferably SiO ₂ raw material such as tetraethyl orthosilicate (TEOS) or silicon oxide powder. In the case of tetraethyl orthosilicate (TEOS), the amount added is more than 0 _ppm and less than 1,000 ppm (more than 0% by mass and 0 .1% by mass or less), and if it is a silicon oxide powder ( _SiO powder), it is more than 0 ppm and 1,000 ppm in the entire raw material powder (garnet-type composite oxide raw material powder + sintering aid). or less (more than 0% by mass and 0.1% by mass or less). If the added amount exceeds 1,000 ppm, there is a possibility that a minute amount of light absorption may occur due to crystal defects due to the excessively contained Si. In the case of silicon oxide powder (SiO ₂ powder), the primary particle size is not particularly limited, but fine powder of less than 1 μm is preferable because the sintering aid can be uniformly dispersed in the starting material.

In the slurry obtained by wet mixing, the particle size distribution of the terbium oxide powder, the yttrium oxide powder, the scandium oxide powder, and the aluminum oxide powder has a single peak, and the D50 value, which is the median diameter of the particle size distribution, is preferably 400 nm or more. is 450 nm or more and 800 nm or less, and the D95 value, which is the value of cumulative 95% by volume from the minimum value side of the particle size distribution, is 2 μm or less, preferably 1 μm or more and 2 μm or less.

As a result of extensive studies by the present inventors, as long as the particle size distribution of the slurry obtained by wet mixing appears as a sharp single peak, the median diameter corresponding to the average particle size is as large as possible, the terbium oxide powder, the oxide The transparency of paramagnetic garnet-type transparent ceramics obtained by sintering a mixed powder of yttrium powder, scandium oxide powder and aluminum oxide powder is improved and stabilized. Specifically, the particle size distribution of the slurry obtained by wet-mixing the terbium oxide powder, yttrium oxide powder, scandium oxide powder, and aluminum oxide powder used has a single peak, and the D50 value, which is the median diameter, is When the particle diameter is 400 nm or more and the D95 value, which is the cumulative value of 95% by volume from the minimum value side of the particle size distribution, is 2 μm or less, the paramagnetic garnet-type transparent ceramics containing terbium and yttrium can be stably and highly It is possible to finish in a transparent state with good reproducibility.

Here, even when the D50 value is less than 400 nm, a transparent paramagnetic garnet-type oxide sintered body containing terbium and yttrium may be obtained. However, the reproducibility is low, for example, the influence of the temperature and humidity of the outside air to which the starting material is exposed, the variation in the particle size of each powder of the starting material to be obtained, the variation in the amount of sintering aid added, etc. , the transparency of the paramagnetic garnet-type oxide sintered body is lowered.
Furthermore, when the D95 value, which is the value of cumulative 95% by volume from the minimum value side of the particle size distribution, exceeds 2 μm, this means that the coarse powders of terbium oxide powder and yttrium oxide powder have a large variation in particle size. The optical quality of the terbium- and yttrium-containing paramagnetic garnet-type oxide sintered body obtained from this starting material rapidly deteriorates. Specifically, the unevenness of the refractive index within the optically effective surface of the obtained transparent ceramics becomes severe, and the quality of the beam transmitted through the transparent ceramics as a magneto-optical material is significantly degraded.

The particle size distribution referred to here is the distribution of the abundance ratio of the particle sizes of the terbium oxide powder, yttrium oxide powder, scandium oxide powder, and aluminum oxide powder, which are the starting materials in a non-agglomerated state in the slurry, For example, it can be determined by acquiring a powder SEM image, measuring each particle size of a plurality of (preferably 20 or more) primary particles appearing on the image data by image analysis, and calculating the average value.

In the present invention, for wet mixing, the particle size distribution of the terbium oxide powder, yttrium oxide powder, scandium oxide powder, and aluminum oxide powder in the slurry obtained by mixing (the particle size distribution is evaluated before drying the slurry) is uniform. It has a peak, the D50 value, which is the median diameter of the particle size distribution, is 400 nm or more, and the D95 value, which is the cumulative 95 volume% value from the minimum value side of the particle size distribution, is managed so that it is 2 μm or less. is preferred. This is carried out by mixing coarse powders of terbium oxide powder and yttrium oxide powder with other fine powders of scandium oxide powder and aluminum oxide powder, dispersing them in a dispersion medium, and wet-mixing them in a ball mill or bead mill. This can be achieved by pulverizing the raw material for a very short period of time.
That is, it is preferable to manage the mixing time of wet mixing as short as possible. Specifically, the mixing time is preferably 1 hour or more and 15 hours or less, more preferably 2 hours or more and 10 hours or less.

The dispersion medium for wet mixing is preferably a lower alcohol having 1 to 3 carbon atoms, more preferably ethanol.

It should be noted that the particle size distribution referred to here is for a slurry that does not contain a binder, and among the organic additives that are finally added to the slurry, only the dispersant may be added (the dispersant may not be added), but it is preferable for the slurry to which no other organic additives are added. In general, various organic additives such as dispersants, binders, lubricants and plasticizers are added to slurry for producing ceramics. Some of these organic additives are suitable for dispersing the oxide particles in the slurry (dispersants, etc.), while others aggregate the oxide particles in the slurry at once (binders, etc.). In particular, as the name suggests, the binder has the effect of strongly binding (aggregating) the oxide particles in the slurry. It is necessary to pay attention to the fact that there is an adverse effect that it is not displayed and correct measurement cannot be performed.

One of the greatest features of the method for producing the paramagnetic garnet-type transparent ceramics of the present invention is the non-homogeneity of the slurry state after mixing. Coarse powders of terbium oxide powder and yttrium oxide powder and fine powders of scandium oxide powder and aluminum oxide powder are used as starting materials, and if the mixing time of wet mixing by a ball mill or bead mill is controlled as short as possible, the result is In addition, the terbium oxide powder and the yttrium oxide powder in the slurry are coarser than the scandium oxide powder and the aluminum oxide powder, and the particle size is non-uniform. In this case, the particles of the terbium oxide powder and the yttrium oxide powder are likely to sediment selectively immediately after the wet mixing is finished and the slurry is allowed to stand. When the particles of terbium oxide powder and yttrium oxide powder start to selectively settle, a sediment layer is formed at the bottom of the slurry, and the particles of scandium oxide powder and aluminum oxide powder remain homogeneously dispersed throughout the slurry. Therefore, the terbium oxide powder and the yttrium oxide powder tend to separate from the scandium oxide powder and the aluminum oxide powder within a few minutes after being left still.

Another feature of the method for producing the paramagnetic garnet-type transparent ceramics of the present invention is that despite the slurry having such non-homogeneous characteristics, a clean single peak is obtained when wet particle size distribution measurement is performed. of particle size distribution can be obtained. The reason for this is not clear, but probably because the difference in particle size (difference in particle size) between the coarse particles of the coarse powder and the fine particles of the fine powder is sufficiently (excessively) large, rather than the fine particles of the fine powder aggregating with each other, The fine particles are more stable when they are adsorbed on the surface of the coarse particles of the coarse powder, and as a result of such adsorption, the particle diameters of the two types of coarse particles, terbium oxide powder and yttrium oxide powder, which are coarse powders, are improved. From the fact that the apparent particle size was detected by wet particle size distribution measurement, it is presumed that an apparently clean single-peak particle size distribution was obtained.

In addition, since the terbium oxide powder and the yttrium oxide powder are coarse powders with sufficiently large particle diameters that there is almost no possibility that they themselves aggregate, a broad particle size distribution derived from secondary aggregation and tertiary aggregation occurs. It may prevent you from doing so. However, when the slurry obtained by mixing the coarse powders of terbium oxide powder and yttrium oxide powder and the fine powders of scandium oxide powder and aluminum oxide powder is allowed to stand, the coarse powders of terbium oxide powder and yttrium oxide powder settle immediately. tend to start. At this time, the fine powder other than the fine powder firmly adsorbed on the oxide of the coarse powder stays in the slurry without settling. Therefore, although the slurry apparently exhibits a clear single-peak particle size distribution, the slurry may undergo phase separation into powder that easily settles and powder that does not easily settle upon standing. In the present invention, it is preferable that the terbium oxide powder and/or the yttrium oxide powder precipitate to form a sediment layer immediately after the slurry is allowed to stand after wet mixing.

As described above, the raw material powder (raw material powder for garnet-type composite oxide + sintering aid) may be added with an organic additive as a dispersant in order to increase its dispersibility. Examples include dispersants, dodecylbenzenesulfonic acid, and polyethylene glycol-based dispersants, but are not particularly limited. In addition, when a binder is used to improve the shape retention of molding, it is preferable to add it at this timing, and polyvinyl alcohol-based, polyacrylic acid-based, polyvinyl acetate-based, and polyvinyl butyral-based binders are exemplified. However, it is not particularly limited as long as the shape retention can be maintained.
As described above, a slurry (molding raw material powder slurry) in which all the raw material powders are uniformly mixed is obtained.

(molding)
Subsequently, molding is performed using the raw material powder slurry for molding so as to obtain a predetermined shape. The molding method includes a wet method and a dry method, but is not particularly limited in the present invention as long as it can be made transparent. Wet molding is exemplified by cast molding, centrifugal cast molding, extrusion molding, and tape molding, but is not particularly limited as long as the desired shape can be obtained. In dry molding, granules are produced from raw material powder slurry and uniaxially press-molded using a jig so as to have a predetermined shape. The method of granulation is exemplified by spray drying, sieving after vibration drying, etc., but is not particularly limited as long as the granule diameter is 2 μm or more and 1000 μm or less. If the granule diameter is less than 2 µm, each granule becomes light and the moldability may deteriorate. On the other hand, if it exceeds 1000 μm, the voids between the granules after molding become large, and there is a possibility that they remain as coarse air bubbles inside the molded body.

In the present invention, it is preferred that the slurry is spray-dried to form a granular raw material, and the granular raw material is used for molding. In this case, a normal press molding process can be preferably used. That is, a very common uniaxial pressing process in which the mold is filled and pressurized from a certain direction, and cold isostatic pressing (CIP) in which the material is sealed and housed in a deformable waterproof container and pressurized with hydrostatic pressure (CIP). A warm isostatic pressing (WIP) process can be suitably used. The applied pressure may be adjusted as appropriate while checking the relative density of the obtained molded body, and is not particularly limited. can be suppressed. Alternatively, a hot pressing process, a discharge plasma sintering process, a microwave heating process, or the like, in which not only the molding process but also sintering is performed at once during molding, can be suitably used. Furthermore, it is also possible to produce a molded body by a cast molding method instead of a press molding method.

(degreasing)
In the production method of the present invention, a normal degreasing step can be suitably used. That is, it is possible to go through a temperature rising degreasing process using a heating furnace. Also, the type of atmosphere gas at this time is not particularly limited, and air, oxygen, hydrogen, etc. can be suitably used. The degreasing temperature is not particularly limited, but if a raw material mixed with an organic additive is used, it is preferable to raise the temperature to a temperature at which the organic component can be decomposed and removed.

(sintering)
In the manufacturing method of the present invention, a general sintering process can be suitably used. That is, a heating sintering process such as a resistance heating method or an induction heating method can be preferably used. The atmosphere at this time is not particularly limited, and sintering in various atmospheres such as inert gas, oxygen gas, hydrogen gas, helium gas, etc., or under reduced pressure (in vacuum) is also possible. However, since it is preferable to ultimately prevent the occurrence of oxygen vacancies, more preferable atmospheres include an oxygen gas atmosphere and a reduced-pressure oxygen gas atmosphere.

The sintering temperature in the sintering step of the present invention is preferably 1440 to 1780°C, particularly preferably 1470 to 1730°C. When the sintering temperature is within this range, densification is promoted while suppressing the precipitation of heterogeneous phases, which is preferable.

The sintering holding time in the sintering step of the present invention is sufficient for several hours, but the relative density of the sintered body must be densified to at least 94%. It is more preferable to keep the sintered body for 10 hours or more to densify the relative density of the sintered body to 99% or more, because the final transparency is improved.

(Hot isostatic pressing (HIP))
In the production method of the present invention, a step of performing a hot isostatic pressing (HIP) treatment can be additionally provided after the sintering step.

At this time, an inert gas such as argon or nitrogen, or Ar--O ₂ can be suitably used as the type of pressurized gas medium. The pressure applied by the pressurized gas medium is preferably 50-300 MPa, more preferably 100-300 MPa. If the pressure is less than 50 MPa, the effect of improving transparency may not be obtained, and if the pressure exceeds 300 MPa, even if the pressure is increased, no further improvement in transparency can be obtained, and the load on the device becomes excessive, which may damage the device. . It is preferable that the applied pressure is 196 MPa or less, which can be processed by a commercially available HIP device, because of its simplicity.

The treatment temperature (predetermined holding temperature) at that time is set in the range of 1100 to 1780°C, preferably 1200 to 1730°C. If the heat treatment temperature exceeds 1780° C., the risk of generating oxygen deficiency increases, which is not preferable. Also, if the heat treatment temperature is less than 1100° C., the effect of improving the transparency of the sintered body is hardly obtained. The holding time of the heat treatment temperature is not particularly limited, but holding for too long increases the risk of generating oxygen deficiency, which is not preferable. Typically, it is preferably set within the range of 1 to 3 hours.

The heater material, heat insulating material, and treatment container for HIP treatment are not particularly limited, but graphite, molybdenum (Mo), tungsten (W), and platinum (Pt) can be suitably used. Gadolinium is also suitable for use. In particular, when the treatment temperature is 1500° C. or lower, platinum (Pt) can be used as the heater material, the heat insulating material, and the treatment container, and the pressurized gas medium can be Ar—O ₂ . It is preferable because it can prevent the occurrence of chipping. When the processing temperature exceeds 1500 ° C., graphite is preferable as a heater material and a heat insulating material. It is preferable to select either yttrium oxide or gadolinium oxide as the heavy container and then fill the container with an oxygen release material so as to minimize the amount of oxygen deficiency generated during the HIP treatment.

(oxidation annealing)
In the manufacturing method of the present invention, oxygen deficiency occurs in the transparent ceramic sintered body obtained after the HIP treatment, and the appearance may be faintly light gray. In that case, it is preferable to perform an oxidation annealing treatment (oxygen deficiency recovery treatment) in an oxygen atmosphere or air at a temperature lower than the HIP treatment temperature, typically 1000 to 1500°C. Although the holding time in this case is not particularly limited, it is preferably selected to be a time longer than a time sufficient to recover oxygen deficiency and a time within which the electricity cost is not wasted due to an unnecessarily long treatment. By the oxidizing annealing treatment, even a transparent ceramic sintered body that has exhibited a faint light gray appearance in the HIP treatment process can be converted into a colorless transparent paramagnetic garnet type transparent ceramic that does not absorb defects. can.

(optical polishing)
In the production method of the present invention, the paramagnetic garnet-type transparent ceramics that have undergone the series of production steps described above are preferably optically polished on both end faces on the optically utilized axis. At this time, the optical surface precision is preferably λ/2 or less, particularly preferably λ/8 or less, when the measurement wavelength λ is 633 nm. The optical loss can be further reduced by appropriately forming an antireflection film on the optically polished surface.

As described above, paramagnetic garnet-type transparent ceramics containing terbium and yttrium can be provided. The transparent ceramics can be used as a Faraday rotator operable in the wavelength range of 0.9 μm to 1.1 μm. This paramagnetic garnet-type transparent ceramic can ensure a Verdet constant of 32 rad/(T·m) or more at a wavelength of 1064 nm by producing the composition under the conditions described above. The Verdet constant can be increased to 36 rad/(T·m) or more by decreasing the concentration x of yttrium (Y) in the above formula (1). When the Verdet constant is 36 rad/(T·m) or more, it is convenient and preferable because it can be replaced with the TGG single crystal, which is an existing material, without changing the design of parts. Also, if the Verdet constant is 32 rad/(T·m) or more, compatibility with an isolator using a TGG single crystal is possible without enlarging the outer shape of the entire isolator by designing and devising the outer cylinder magnet. preferable. Furthermore, this paramagnetic garnet-type transparent ceramic can be finished with a thermal conductivity of 4.8 W/m·K or more by manufacturing it with the composition under the conditions described above. The thermal conductivity can be measured according to JIS R1611 and can be evaluated by the laser flash method.

[Magneto-optical device]
Furthermore, in the present invention, since it is assumed that paramagnetic garnet-type transparent ceramics are used as a magneto-optic material, a magnetic field is applied to the paramagnetic garnet-type transparent ceramics in parallel with its optical axis, and then a polarizer, It is preferable to configure and utilize the analyzer as a magneto-optical device by setting the optical axes of the analyzer and the analyzer so that their optical axes are shifted from each other by 45 degrees. That is, the paramagnetic garnet-type transparent ceramics produced according to the present invention are suitable for use in magneto-optical devices, particularly as Faraday rotators of optical isolators with wavelengths of 0.9 to 1.1 μm.

FIG. 1 is a schematic cross-sectional view showing an example of an optical isolator, which is an optical device having a Faraday rotator made of paramagnetic garnet-type transparent ceramics manufactured according to the present invention as an optical element. In FIG. 1, an optical isolator 100 comprises a Faraday rotator 110 made of paramagnetic garnet-type transparent ceramics manufactured according to the present invention. is provided. Also, in the optical isolator 100, it is preferable that the polarizer 120, the Faraday rotator 110, and the analyzer 130 are arranged in this order, and the magnet 140 is mounted on at least one of the side surfaces thereof.

Also, the optical isolator 100 can be suitably used in an industrial fiber laser device. In other words, it is suitable for preventing the reflected light of the laser light emitted from the laser light source from returning to the light source and causing the oscillation to become unstable.

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the examples.
The average particle size of each powder of the starting material is the volume average particle size (cumulative average size D50 (median size)) measured by Microtrac (laser diffraction and scattering method), which was measured by Microtrac MT3300WXII manufactured by Nikkiso Co., Ltd.

[Examples 1 to 10, Comparative Examples 1 to 8]
As starting materials, terbium oxide fine powder (Tb ₄ O ₇ ), yttrium oxide fine powder (Y ₂ O ₃ ), scandium oxide fine powder (Sc ₂ O ₃ ) manufactured by Shin-Etsu Chemical Co., Ltd.; Coarse terbium oxide powder (Tb ₄ O ₇ ) and coarse yttrium oxide powder (Y ₂ O ₃ ) were obtained. These average particle sizes were 200 nm, 200 nm and 600 nm in the above order from Shin-Etsu Chemical Co., Ltd. (these are referred to as fine powders), and those from China were all 4 μm (these are coarse powder). Aluminum oxide powder (Al ₂ O ₃ , average particle size 300 nm; fine powder) manufactured by Taimei Chemical Co., Ltd. was also obtained, and liquid tetraethyl orthosilicate (TEOS) manufactured by Kishida Chemical Co., Ltd. was also obtained. Purity was 99.95% by mass or more for the powder raw materials and 99.999% by mass or more for the liquid raw materials.
For the terbium and yttrium oxide powders among the above starting materials, coarse powders are used, and the mixing ratio is adjusted so that the five types of final compositions shown in Table 1 are obtained (that is, terbium, yttrium, scandium and aluminum They were weighed and mixed so that the number of moles would be the molar ratio of each composition shown in Table 1), and then TEOS was weighed and added so that the amount to be added would be the mass % shown in Table 1 in terms of SiO ₂ . A composite oxide raw material for wet mixing was prepared (the combination of oxide powders (Tb, Y--Sc, Al) of the starting raw materials is called coarse powder-fine powder). In addition, each oxide powder of terbium and yttrium was changed from coarse powder to fine powder, and Oxide Raw Material No. A composite oxide raw material for wet mixing having the same composition as that of No. 3 was prepared. 6 (this is referred to as a fine powder-fine powder combination (Tb, Y--Sc, Al) of the starting raw material oxide powders). In this way, a total of six types of composite oxide raw materials for mixing were prepared.

(wet mixing)
The prepared composite oxide raw materials for wet mixing were dispersed and mixed (wet mixed) in ethanol with an alumina ball mill device while taking care to prevent mutual mixing. At this time, a total of 18 types of mixed raw material slurries were prepared by changing the mixing time for each raw material at three levels of 5 hours, 10 hours, and 20 hours.
For each slurry, after wet mixing, the presence or absence of the formation of a sediment layer immediately after standing was observed.

Further, the particle size distribution of each obtained slurry was measured by the following method.
(Method for measuring particle size distribution)
The particle size distribution of the slurry was measured as follows using Microtrac MT3300WXII manufactured by Nikkiso Co., Ltd. with reference to JIS Z8825-2:2013.
A wet mode with a measurement range of 0.021 to 2000 μm (132 ch) was selected, and ethanol was used as the circulating solvent. The slurry to be measured was dropped here, and the particle size distribution was measured under the measurement conditions of 30 seconds×2 times without applying ultrasonic cleaning. As a representative value of the refractive index, the refractive index value when the components of the mixed composition form a solid solution with a garnet structure is substituted. By the way, no special dispersant was added to ethanol, but unlike water, the fine powder does not aggregate easily in ethanol, so it was judged that there was no problem in measuring the particle size distribution.
In addition, it was confirmed whether the state of the measured particle size distribution was a single peak or multiple peaks (split). Oxide raw material no. 3, No. The particle size distribution of the slurry for each of the six mixing times is shown in Figures 2 and 3. In FIG. 2, the mixing time of 5 hours (5 h) is Example 5, the mixing time of 10 hours (10 h) is Example 6, and the mixing time of 20 hours (20 h) is Comparative Example 3. In FIG. 3, the mixing time is 5 hours. (5 hours) is Comparative Example 6, 10 hours (10 hours) is Comparative Example 7, and 20 hours (20 hours) is Comparative Example 8. Oxide raw material No. in FIG. In 3, the particle size distribution of all slurries had a single peak. Oxide raw material No. in FIG. 6, the particle size distribution was split between 5 hours and 10 hours of mixing, and the particle size distribution of 20 hours had a single peak.
In addition, the D50 value, which is the median diameter of the particle size distribution, and the D95 value, which is the cumulative 95% by volume value from the minimum value side of the particle size distribution, were extracted from the data obtained by the measurement.

(Molding and degreasing)
After that, the obtained slurry was subjected to a spray drying treatment to prepare a granular raw material having an average particle size of 20 μm. The obtained 18 types of granular materials were each subjected to uniaxial press molding and isostatic pressing at a pressure of 198 MPa to obtain cylindrical CIP molded bodies. In order to confirm manufacturing stability, three samples were molded under each condition. The resulting compact was degreased in a muffle furnace at 1000° C. for 3 hours to obtain a degreased compact.
(sintering)
Subsequently, the degreased compacts were placed in a vacuum sintering furnace and treated at 1500 to 1600° C. for 3 hours to obtain a total of 18 types of sintered compacts. The combination of oxide powders (Tb, Y—Sc, Al) of the starting materials is fine powder-fine powder compacts at a lower sintering temperature, and coarse powder-fine powder compacts at a higher sintering temperature. processed. As a result, the sintered relative densities of all samples fell within the range of 94.5 to 98%.
(HIP and oxidation annealing)
Each sintered body thus obtained was placed in a HIP furnace made of a carbon heater, and HIP-treated under the conditions of 200 MPa, 1600° C. and 2 hours in Ar. Almost no graying (absorption of oxygen deficiency) was observed in any of the obtained sintered bodies. However, just to make sure, each ceramic sintered body obtained was annealed at 1450° C. for 30 hours in an atmospheric heating furnace while controlling each lot to sufficiently recover oxygen deficiency. In this way, a total of 18 types of sintered bodies of Examples and Comparative Examples were prepared, three sets each.
(grinding and polishing)
Subsequently, each of the obtained ceramic sintered bodies was ground and polished so as to have a rod (cylindrical) shape with a diameter of 5 mm and a length of 25 mm. 8 (in the case of measurement wavelength λ=633 nm) for final optical polishing.

The total light transmittance, forward scattering rate, and extinction ratio of the transparent ceramic samples obtained as described above were measured as follows.
(Method for measuring total light transmittance and forward scattering rate)
Total light transmittance and forward scattering rate were measured with reference to JIS K7105 (ISO 13468-2:1999) and JIS K7136 (ISO 14782:1999).
Measurement was performed at a wavelength of 1064 nm using a spectrophotometer V-670 manufactured by JASCO Corporation. First, the measurement of the total light transmittance is carried out by irradiating light dispersed by a spectroscope without setting a work (sample) on the spectrophotometer V-670, and applying the light with an integrating sphere set in advance in the device. A detector receives the collected light. The obtained illuminance is assumed to be I ₀ , and then the workpiece is set in the apparatus, and this time the spectrally divided light is incident on the workpiece, and the transmitted light is again collected by the integrating sphere and received by the detector. The resulting illuminance was determined by the following equation as I.

Total light transmittance (%/25 mm) = I/I ₀ ×100

Next, the forward scattering rate was measured using the same measurement system except that the reflecting plate on the back of the integrating sphere was removed from the above-mentioned state in which the work was set. is again collected by the integrating sphere and received by the detector. The obtained illuminance represents the scattering component other than the linear transmission component, which was determined as _IS by the following equation.

Forward scattering rate (%/25 mm) = I _S /I ₀ ×100

In addition, in order to consider the effect of reproducibility and variation, each of the 18 types of samples prepared was measured three times, and the average value was calculated to calculate the total light transmittance and forward scattering rate of each sample. and

(Method for measuring extinction ratio)
The extinction ratio as a Faraday rotator was measured in the following manner with reference to JIS C5877-2:2012.
The extinction ratio was measured using an optical system made in-house using a light source made by NKT Photonics, a collimator lens, a polarizer, a work stage, an analyzer, a power meter made by Gentec, and a Ge photodetector, and a beam of light with a wavelength of 1064 nm. The light is transmitted through the sample with a large diameter of 3 mmφ, and in this state, the light intensity I ₀ ' (maximum laser light intensity) when the polarization plane of the analyzer is aligned with that of the polarizer is measured. Then, after rotating the polarization plane of the analyzer by 90 degrees and making it orthogonal to the polarization plane of the polarizer, the received light intensity I' (minimum value as the laser light intensity) was measured again, and based on the following formula was obtained by calculation.

Extinction ratio (dB) = -10 x log ₁₀ (I'/I ₀ ')

If the beam diameter is made larger than 3 mm, the skirt of the beam begins to be kicked at the outer periphery of the sample with a diameter of 5 mm.
The extinction ratio was also measured for each of the 18 kinds of samples prepared in the same manner as described above, and the average value was taken as the extinction ratio of each sample.
Table 2 shows the above results.

From the above results, in producing the paramagnetic garnet-type transparent ceramics of the present invention, first, the combination of oxide powders (Tb, Y--Sc, Al) as starting materials was fine powder-fine powder oxide raw material No. 1. In Group 6 (Comparative Examples 6 to 8), the total light transmittance of the transparent ceramics obtained was low, the forward scattering rate was large, and the optical quality was poor regardless of the mixing time of the slurry. .
The combination (Tb, Y--Sc, Al) of the oxide powders of the starting materials is coarse powder-fine powder oxide raw material No. Regarding Groups 1 to 5, when the wet mixing time was 20 hours (Comparative Examples 1 to 5), the transparent ceramics obtained had a forward scattering rate of 1% or more and an extinction ratio of less than 40 dB, indicating poor optical quality. was bad.
Oxide raw material no. When the wet mixing time of Groups 1 to 5 is 10 hours or less (Examples 1 to 10), the obtained transparent ceramics have a total light transmittance of 84% or more, a forward scattering rate of less than 1%, and an extinction ratio of 40 dB or more. Thus, the optical quality was good.

When these examples and comparative examples are arranged from the viewpoint of the particle size distribution of the slurry, the D50 value, which is the median diameter, is 400 nm or more, and the D95, which is the cumulative value of 95% by volume from the minimum value side of the particle size distribution. When the value is 2 μm or less (Examples 1 to 10), all optical quality is good, and conversely, the D50 value is 350 nm or less (Comparative Examples 1 to 5, 7, 8), or the D95 value is 3 μm or more (Comparative All of Example 6) had poor optical quality.
That is, a combination of oxide powders (Tb, Y—Sc, Al) as starting materials is weighed as a coarse powder and a fine powder at a desired composition ratio and wet-mixed to prepare a slurry, and the particle size distribution of the slurry is uniform. Paramagnetic garnet-type transparent ceramics with high optical quality by molding, sintering, and annealing in a predetermined process when one peak is reached, the D50 value is 400 nm or more, and the D95 value is 2 μm or less. can be produced stably with good yield.

[Post-treatment of Examples 1, 3, 5, 7 and 9]
For the transparent ceramic samples (three sets each) of Examples 1, 3, 5, 7, and 9 prepared in the manner described above, antireflection coatings (AR coat) was coated. The Verdet constant of the obtained transparent ceramic sample with AR coating was measured in the following manner.

(Method for measuring Verdet constant)
The Verdet constant V was obtained based on the following formula. For the magnitude (H) of the magnetic field applied to the sample, a value calculated by simulation from the dimensions of the measurement system, residual magnetic flux density (Br) and coercive force (Hc) was used.
θ=V×H×L
(where 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 (in this case, 0 .025 m).)
The average value of the Verdet constants of three samples prepared under each condition was taken as the Verdet constant under each condition.
The obtained results are summarized in Table 3. It was confirmed that the Verdet constant of 32 rad/(T·m) or more was ensured in any of the examples.

Although the present invention has been described with the above embodiments, the present invention is not limited to the above embodiments, and other embodiments, additions, changes, deletions, etc. can be conceived by those skilled in the art. It is included in the scope of the present invention as long as it can be changed within the scope and the effects of the present invention can be exhibited in any aspect.

100 optical isolator 110 Faraday rotator 120 polarizer 130 analyzer 140 magnet

Claims (7)

Terbium oxide powder, yttrium oxide powder, scandium oxide powder, and aluminum oxide powder as starting materials and _SiO2 raw material as a sintering aid are wet-mixed to form a slurry, and after molding using the slurry, the obtained The molded body is degreased and sintered, and the following formula (1)

₍ Tb1 _{-xyYxScy ) 3 (} Al1 _{-zScz ) 5O12} (1)
(Wherein, 0.05 ≤ x ≤ 0.4, 0 ≤ y < 0.08, 0.52 < 1-xy < 0.95, 0 ≤ z < 0.2, 0.001 < y + z < 0.2.)

Manufacture of paramagnetic garnet _- type transparent ceramics to obtain paramagnetic garnet-type transparent ceramics which is a sintered body of a composite oxide represented by in the method
The average particle size of the terbium oxide powder and the yttrium oxide powder as the starting materials is 3 μm or more, and the average particle size of the scandium oxide powder and the aluminum oxide powder as the starting materials is less than 1 μm, and the terbium oxide in the slurry The particle size distribution of the powder, the yttrium oxide powder, the scandium oxide powder, and the aluminum oxide powder has a single peak, the D50 value, which is the median diameter of the particle size distribution, is 400 nm or more, and the minimum value side of the particle size distribution A method for producing paramagnetic garnet-type transparent ceramics, characterized in that the D95 value, which is the cumulative value of 95% by volume, is 2 μm or less. 2. The method for producing paramagnetic garnet-type transparent ceramics according to claim 1, wherein said wet mixing is by a ball mill or a bead mill. 3. The method for producing paramagnetic garnet-type transparent ceramics according to claim 2, wherein the mixing time in the ball mill or bead mill is 1 hour or more and 15 hours or less. 4. The method for producing paramagnetic garnet-type transparent ceramics according to any one of claims 1 to 3, wherein the dispersion medium for wet mixing is a lower alcohol having 1 to 3 carbon atoms. The method for producing paramagnetic garnet-type transparent ceramics according to any one of claims 1 to 4, wherein the particle size distribution is for slurry containing no binder. The slurry according to any one of claims 1 to 5, wherein when left to stand after wet mixing, the terbium oxide powder and/or yttrium oxide powder precipitate immediately after that to form a sediment layer. A method for producing magnetic garnet-type transparent ceramics. The method for producing paramagnetic garnet-type transparent ceramics according to any one of claims 1 to 6, wherein the slurry is spray-dried to form a granular raw material, and the granular raw material is used for molding.