Method for manufacturing ferromagnetic garnet type transparent ceramics

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

[0001] The present invention relates to a method for manufacturing ferromagnetic garnet-type transparent ceramics, and more particularly to a method for manufacturing garnet-type transparent ceramics containing terbium and yttrium, which are suitable for constituting magneto-optical devices such as optical isolators.

Background Art

[0002] In recent years, due to the increasing output power of fiber lasers, the spread of laser processing machines using such fiber lasers has been remarkable. By the way, in a laser light source incorporated in a laser processing machine, when light from the outside is incident, the resonance state becomes unstable and the oscillation state is disturbed. In particular, when the oscillated light is reflected by an intermediate optical system and returns to the light source, the oscillation state is greatly disturbed. To prevent this, an optical isolator is usually provided on the light output side of the light source, such as between the laser light source and the optical fiber.

[0003] An optical isolator includes a Faraday rotator, a polarizer disposed on the light incident side of the Faraday rotator, and an analyzer disposed on the light output side of the Faraday rotator. Further, the Faraday rotator is used by applying a magnetic field parallel to the traveling direction of light. At this time, the polarization component of light rotates only in a certain direction whether it advances or retreats in the Faraday rotator. Furthermore, the Faraday rotator is adjusted to a length such that the polarization component of light is rotated exactly 45 degrees. Here, if the polarization planes of the polarizer and the analyzer are shifted by 45 degrees in the rotation direction of the advancing light, the polarization of the advancing light coincides at the polarizer position and the analyzer position, so it is transmitted. On the other hand, the polarization of the backward light rotates 45 degrees in the reverse rotation to the deviation angle direction of the polarization plane of the polarizer that is shifted by 45 degrees from the analyzer position. Then, the polarization plane of the return light at the polarizer position is shifted by 45 degrees - (-45 degrees) = 90 degrees with respect to the polarization plane of the polarizer and cannot pass through the polarizer. In this way, it functions as an optical isolator that transmits and emits the advancing light and blocks the backward return light.

[0004] As a material used as the Faraday rotator constituting the above optical isolator, conventionally, TGG crystal (Tb 3 Ga 5 O 12 ) and TSAG crystal ((Tb (3-x) Sc x )Sc 2 Al 3 O 12 ) have been known (Japanese Patent Application Laid-Open No. 2011-213552 (Patent Document 1), Japanese Patent Application Laid-Open No. 2002-293693 (Patent Document 2)). TGG crystal is currently widely used 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, and this is also a material that can be mounted on a fiber laser device without any problem. However, since Sc is an extremely expensive raw material, its adoption has not progressed from the perspective of manufacturing cost.

[0005] Other than the above, as a Faraday rotator having a larger Verdet constant than TSAG, TAG crystal (Tb 3 Al 5 O 12 ) has also been known for a long time. However, since TAG crystal is a decomposition-melting type crystal, there is a restriction that the perovskite phase is first generated at the solid-liquid interface and then the TAG phase is generated. That is, the garnet phase and the perovskite phase of TAG crystal can only be crystallized in a state of always being mixed, and the growth of high-quality and large-sized TAG crystal has not been realized.

[0006] In Japanese Patent No. 3642063 (Patent Document 3) and Japanese Patent No. 4107292 (Patent Document 4), as a means for suppressing this mixed crystal, a method of preferentially depositing the perovskite phase, which is the primary phase, in a porous medium by making the polycrystalline raw material rod for FZ growth or the seed crystal porous has been proposed. However, in reality, as the melting position moves, the position where the perovskite phase is likely to precipitate also moves. Therefore, it was essentially impossible to completely suppress the precipitation of the perovskite phase just by making only the interface between the seed crystal and the polycrystalline raw material rod porous.

[0007] Under such constraints, recently, it has been disclosed that a dense ceramic sintered body with a composition of (Tb x Y 1-x ) 3 Al 5 O 12 (x = 0.5 to 1.0) has a higher extinction ratio than existing TGG crystals (improved from the existing 35 dB to 39.5 dB or more), and the insertion loss can also be reduced (improved from the existing 0.05 dB to 0.01 to 0.05 dB) (Yan Lin Aung, Akio Ikesue, Development of optical grade (Tb x Y 1-x ) 3 Al 5 O 12 ceramics as Faraday rotator material, J.Am.Ceram.Soc.,(2017),100(9),4081 - 4087 (Non - Patent Document 1)). Since the material disclosed in this Non - Patent Document 1 is first a ceramic, there is no precipitation of perovskite heterophase, which was a problem with TGG crystals. Furthermore, by substituting a part of Tb ions with Y ions, further reduction of loss is made possible, and it is a material capable of obtaining an extremely high - quality garnet - type Faraday rotator.

[0008] Furthermore, Japanese Patent Application Laid - Open No. 2019 - 199386 (Patent Document 5) discloses (Tb 1-x-y Y x Sc y ) 3 (Al 1-z Sc z ) 5 O 12(wherein 0.05 ≦ x < 0.45, 0 < y < 0.1, 0.5 < 1 - x - y < 0.95, and 0.004 < z < 0.2). A paramagnetic garnet-type transparent ceramic having such a composition is disclosed. This material has a composition similar to that of Non-Patent Document 1, but is different in that Sc is significantly added. The material has an extinction ratio of 40 dB or more, which is further improved compared to Non-Patent Document 1, and even when irradiated with a 100 W laser, the amount of change in the focal position due to the thermal lens is small, and it can be used as a practical optical isolator that can withstand practical use. It is a truly practical paramagnetic garnet-type transparent ceramic that is easy to scale up because it is made of ceramics.

[0009] By the way, Japanese Patent No. 6119528 (Patent Document 6) discloses a method for producing a transparent sesquioxide sintered body. In the particle size distribution of oxide particles of rare earth elements (when the particles are aggregated and secondary particles are formed, this is the particle size distribution of the secondary particles), a raw material powder in which the cumulative 2.5 volume% particle diameter (D2.5 value) from the minimum value side is 180 nm or more and 2000 nm or less, and a raw material powder in which the D2.5 value is 180 nm or more and 280 nm or less and the median diameter D50 value is 950 nm or less are used. It is said that a truly translucent transparent sintered body without residual bubbles that inhibit translucency can be stably provided.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Non-Patent Literature

[0011]

Non-Patent Literature 1

Summary of the Invention

Problems to be Solved by the Invention

[0012] However, when the inventors actually conducted retests under the conditions of Non-Patent Literature 1 and Patent Literature 5, it was confirmed that the reproducibility was quite poor, and it was difficult to obtain a high-quality ceramic sintered body with insertion loss smaller than that of TGG crystals.

[0013] In addition, the transparent sesquioxide sintered body in Patent Literature 6 has a different composition and crystal structure from the paramagnetic garnet-type transparent ceramic sintered body. However, in order to stably produce a transparent sintered body with good reproducibility, it is suggested that it is important to control the particle size and particle size distribution of the raw material powder used. However, so far, no information about the particle size and particle size distribution of the raw material powder for finishing the paramagnetic garnet-type transparent ceramic sintered body into a highly transparent sintered body with good reproducibility and stability has been disclosed at all.

[0014] 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 manufacturing a truly practical paramagnetic garnet-type transparent ceramic, which is a sintered body of a paramagnetic garnet-type oxide containing terbium and yttrium, has extremely high transparency, and has extremely high manufacturing reproducibility and stability.

Means for Solving the Problems

[0015] In order to achieve the above object, the present inventors have intensively studied a method for stably producing a sintered body of a paramagnetic garnet-type oxide containing terbium and yttrium based on the findings of the above-known examples, and have thus completed the present invention.

[0016] That is, the present invention provides a method for producing the following paramagnetic garnet-type transparent ceramics. 1. Terbium oxide powder, yttrium oxide powder, scandium oxide powder, and aluminum oxide powder as starting materials, and SiO as a sintering aid 2 are wet-mixed with the raw materials to form a slurry. After molding using the slurry, the obtained molded body is degreased and sintered to obtain a 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, 0.0494 ≦x≦0.4, 0.001 < y < 0.004, 0.596 < 1 - x - y < 0.9496 , 0.0005 < z < 0.004, 0.0015 < y + z < 0.008.) is a sintered body of a composite oxide represented by the formula, and in the method for producing paramagnetic garnet-type transparent ceramics for obtaining paramagnetic garnet-type transparent ceramics containing more than 0% by mass and 0.1% by mass or less of SiO as a sintering aid 2 , A method for manufacturing paramagnetic garnet-type transparent ceramics, characterized in that the average particle diameters of the terbium oxide powder and yttrium oxide powder as the starting materials are each 3 μm or more, the average particle diameters of the scandium oxide powder and aluminum oxide powder as the starting materials are each less than 1 μm, the particle size distribution of the terbium oxide powder, yttrium oxide powder, scandium oxide powder and aluminum oxide powder in the slurry has a single 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 value of 95% by volume accumulated from the minimum value side of the particle size distribution is 2 μm or less. 2. The method for manufacturing paramagnetic garnet-type transparent ceramics according to 1, wherein the wet mixing is performed by a ball mill or a bead mill. 3. The method for manufacturing paramagnetic garnet-type transparent ceramics according to 2, wherein the mixing time by the ball mill or the bead mill is 1 hour or more and 15 hours or less. 4. The method for manufacturing paramagnetic garnet-type transparent ceramics according to any one of 1 to 3, wherein the dispersion medium for the wet mixing is a lower alcohol having 1 to 3 carbon atoms. 5. The method for manufacturing paramagnetic garnet-type transparent ceramics according to any one of 1 to 4, wherein the particle size distribution is for a slurry not containing a binder. 6. The method for manufacturing paramagnetic garnet-type transparent ceramics according to any one of 1 to 5, wherein when the slurry is allowed to stand after wet mixing, the terbium oxide powder and / or yttrium oxide powder settle immediately thereafter to form a deposited layer. 7. The method for manufacturing 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.

Advantages of the Invention

[0017] According to the present invention, it becomes possible to stably and highly reproducibly finish a paramagnetic garnet-type oxide sintered body containing terbium and yttrium in a highly transparent state, and a truly practical paramagnetic garnet-type oxide transparent ceramic applicable to a high-power laser device can be provided.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0019] Hereinafter, the configuration of a method for manufacturing a paramagnetic garnet-type transparent ceramic according to the present invention will be described. The method for manufacturing a paramagnetic garnet-type transparent ceramic of the present invention includes terbium oxide powder, yttrium oxide powder, scandium oxide powder, and aluminum oxide powder as starting materials, and SiO as a sintering aid 2 The raw materials are wet-mixed to form a slurry, and after molding using the slurry, the obtained molded body is degreased and sintered to obtain 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 < 0.2, 0.001 < y + z < 0.2.) It is a sintered body of a composite oxide represented by, and contains SiO as a sintering aid in an amount of more than 0 mass% and 0.1 mass% or less. 2 In a method for producing a paramagnetic garnet-type transparent ceramic for obtaining a paramagnetic garnet-type transparent ceramic containing more than 0 mass% and 0.1 mass% or less of 2 as a sintering aid, (a) The average particle diameter of each of the terbium oxide powder and yttrium oxide powder of the starting materials is 3 μm or more, and the average particle diameter of each of the scandium oxide powder and aluminum oxide powder of the starting materials is less than 1 μm, (b) The particle size distribution of the terbium oxide powder, yttrium oxide powder, scandium oxide powder and aluminum oxide powder in the slurry has a single 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 value of 95% by volume in cumulative from the minimum value side of the particle size distribution is 2 μm or less.

[0020] (Transparent ceramic) The transparent ceramic produced by the present invention is composed of 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 compositional formula (1). When producing a paramagnetic garnet-type transparent ceramic having a composition within the range represented by the above formula (1), the optical scattering is extremely small, the distortion and absorption are also extremely small, and it can have a sufficient Verdet constant as a Faraday rotator.

[0021] Specifically, by adding terbium (Tb) in the concentration range represented by formula (1), a sufficient Verdet constant can be ensured, and by adding yttrium (Y) in the concentration range represented by formula (1), suppression of heterogeneous phases and minimization of internal strain can be ensured. Further, by adding scandium (Sc) in the concentration range represented by formula (1), complete disappearance of heterogeneous phases is achieved. Furthermore, by adding aluminum (Al) in the concentration range represented by formula (1), a sufficient Verdet constant is ensured and a relatively high thermal conductivity is imparted.

[0022] The numerical ranges for x, y, and z in formula (1) are as follows in detail. 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 within this range, the perovskite-type heterogeneous phase can be reduced to a level where it cannot be detected by X-ray diffraction (XRD) analysis.

[0023] When x is less than 0.05, the effect of substituting a part of terbium with yttrium cannot be obtained, and it becomes substantially the same as the condition for producing TAG. Therefore, it is not preferable because it is difficult to stably manufacture a high-quality ceramic sintered body with low scattering and low absorption. Also, when x is greater than 0.4, the Verdet constant at a wavelength of 1064 nm is less than 32 rad / (T·m), which is not preferable. Furthermore, when the relative concentration of terbium becomes excessively low, the total length required to rotate the laser beam with a wavelength of 1064 nm by 45 degrees becomes longer than 25 mm, making the manufacturing difficult, so it is not preferable.

[0024] In formula (1), the range of y is 0 ≤ y < 0.08, preferably 0.001 < y < 0.004, and more preferably 0.002 < y < 0.004. When y is within 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 due to the homogeneity of the sintered body and grain boundary scattering.

[0025] When y is 0.08 or more, while the effect of suppressing the precipitation of the perovskite-type heterogeneous phase or the alumina heterogeneous phase is saturated and unchanged, uneven sintering, residual sintering strain, or residual grain boundary scattering occurs due to the excessive effect of the sintering suppression effect of scandium. As a result, a local decrease in the extinction ratio and a decrease in the average value of the thermal conductivity occur, which is not preferable.

[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] (1) In the formula, the range of z is 0 ≦ z < 0.2, preferably 0.001 < z < 0.004, and more preferably 0.02 ≦ z < 0.004. When z is within 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 excessive decrease in thermal conductivity due to the homogeneity of the sintered body and grain boundary scattering.

[0028] When z is 0.2 or more, while the effect of suppressing the precipitation of the perovskite-type heterogeneous phase or alumina heterogeneous phase is saturated and does not change, uneven sintering, residual sintering strain, or residual grain boundary scattering occurs due to the excessive effect of the sintering suppression effect of scandium. As a result, local decrease in the extinction ratio and decrease in the average value of thermal conductivity occur, which is not preferable.

[0029] (1) In the formula, the range of y + z is 0.001 < y + z < 0.2, more preferably 0.002 < y + z < 0.005, and even more preferably 0.003 < z < 0.005. When y + z is within 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 excessive decrease in thermal conductivity due to the homogeneity of the sintered body and grain boundary scattering.

[0030] When y + z is 0.001 or less, the risk of precipitation of the perovskite-type heterogeneous phase or alumina heterogeneous phase increases, which is not preferable. When y + z is 0.2 or more, while the effect of suppressing the precipitation of the perovskite-type heterogeneous phase or alumina heterogeneous phase is saturated and does not change, uneven sintering, residual sintering strain, or residual grain boundary scattering occurs due to the excessive effect of the sintering suppression effect of scandium. As a result, local decrease in the extinction ratio and decrease in the average value of thermal conductivity occur, which is not preferable.

[0031] By the way, the paramagnetic garnet-type transparent ceramics obtained in the present invention contain, as the main component, components having a composition within the range represented by the formula (1), and as the sub-component, SiO that serves as a sintering aid 2 is contained in a range of 0.1 mass% or less, with 0.1 mass% as the limit. As the sintering aid, SiO 2When a trace amount is added, precipitation of perovskite-type heterophase, alumina heterophase, etc. is suppressed, so that the transparency of the paramagnetic garnet-type transparent ceramics is further improved. Furthermore, the trace-added SiO 2 is vitrified 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, when more than 0.1% by mass of SiO 2 is added, when a 100 W laser beam with a beam diameter of 1.6 mm at a wavelength of 1064 nm is incident on a paramagnetic garnet-type transparent ceramic with a length (optical path length) of 25 mm, the change amount of the beam diameter exceeds 10%, which is not preferable.

[0032] Here, "contained as a main component" means containing 90% by mass or more of the complex oxide represented by the above formula (1). The content of the complex oxide represented by the formula (1) is preferably 99% by mass or more, more preferably 99.9% by mass or more, still more preferably 99.99% by mass or more, and particularly preferably 99.999% by mass or more.

[0033] In addition, the paramagnetic garnet-type transparent ceramics obtained in the present invention are composed of the above main component and sub-components, but may further contain other elements. Examples of other elements include rare earth elements such as lutetium (Lu) and cerium (Ce), or various impurity groups such as sodium (Na), calcium (Ca), magnesium (Mg), phosphorus (P), tungsten (W), molybdenum (Mo), etc.

[0034] When the total amount of Tb and Y is 100 parts by mass, the content of other elements is preferably 10 parts by mass or less, more preferably 0.1 part by mass or less, and particularly preferably 0.001 part by mass or less (substantially zero).

[0035] (Starting materials) As starting materials used in the present invention, oxide powders of terbium, yttrium, scandium, and aluminum (i.e., terbium oxide powder, yttrium oxide powder, scandium oxide powder, and aluminum oxide powder) are utilized. These are referred to as raw material powders for garnet-type composite oxides. The purity of the raw material powders for garnet-type composite oxides is preferably 99.9 mass% or more, and particularly preferably 99.99 mass% or more.

[0036] In the present invention, the terbium oxide powder, yttrium oxide powder, scandium oxide powder, and aluminum oxide powder as starting materials are precisely weighed so as to have the composition of the composite oxide represented by the above formula (1) as they are, or a mixed powder prepared by precisely weighing and mixing these is used for the production of paramagnetic garnet-type transparent ceramics. When each constituent element of the finally synthesized paramagnetic garnet-type transparent ceramics (oxide sintered body) containing terbium and yttrium is precisely weighed as an individual oxide raw material and then mixed, it is preferable because the weighing accuracy is much higher than that by mixing methods such as coprecipitation.

[0037] Note that various organic additives may be added to the oxide powder raw materials used in the present invention for the purpose of quality stability and yield improvement in the subsequent ceramic manufacturing process. In the present invention, these are not particularly limited. That is, various dispersants, binders, lubricants, plasticizers, etc. can be suitably used. However, as these organic additives, it is preferable to select high-purity types that do not contain unnecessary metal ions. Also, the addition order of each organic additive needs to be appropriately designed so as not to hinder the control of the properties (such as particle size distribution) of the raw material to be manufactured.

[0038] Among the starting materials, particularly for terbium oxide powder and yttrium oxide powder, those with a coarse powder having an average particle diameter of 3 μm or more, preferably 3 μm or more and 6 μm or less before mixing are selected. By doing so, the specific surface areas of these two types of oxide powders (terbium oxide powder and yttrium oxide powder) can be extremely reduced, thereby minimizing the effects of adsorbed moisture, adsorbed gas, and valence change during heating. As a result, it becomes possible to precisely weigh and mix each oxide element so as to achieve exactly the garnet composition, which is preferable. Furthermore, regarding the terbium oxide powder, it is preferable because a sharp increase in the bulk density of the powder due to valence change during heating can be suppressed.

[0039] Also, among the starting materials, for scandium oxide powder and aluminum oxide powder, those with a fine powder having an average particle diameter of less than 1 μm, preferably 200 nm or more and 600 nm or less before mixing are selected. This promotes the sinterability when sintering the mixed raw materials, so that even if coarse powder of terbium oxide powder and yttrium oxide powder is used, the sinterability of the entire mixed raw materials is maintained.

[0040] Note that the average particle diameter mentioned here refers to the average value of the primary particle diameters in a state where the oxide raw material powder of the starting material is not aggregated. For example, it can be determined by obtaining a powder SEM image and measuring the particle diameters of a plurality of (preferably 20 or more) primary particles shown on the image data by image analysis and calculating the average value.

[0041] (Wet mixing) The terbium oxide powder, yttrium oxide powder, scandium oxide powder, and aluminum oxide powder as the precisely weighed starting materials, and SiO as a sintering aid 2 are wet-mixed with the raw material to form a slurry. The wet mixing is a process of dispersing all of the starting materials and the SiO as a sintering aid 2 in a dispersion medium and mixing them, and it is preferably carried out using a ball mill or a bead mill.

[0042] SiO as a sintering aid 2Raw materials include, for example, tetraethyl orthosilicate (TEOS), or SiO such as silicon oxide powder 2 Raw materials are preferred. When the raw material is tetraethyl orthosilicate (TEOS), in terms of SiO 2 conversion, the amount is more than 0 ppm and 1,000 ppm or less (more than 0% by mass and 0.1% by mass or less) in the total raw material powder (raw material powder for garnet-type composite oxide + sintering aid). When it is silicon oxide powder (SiO 2 powder), it is preferably an amount that is more than 0 ppm and 1,000 ppm or less (more than 0% by mass and 0.1% by mass or less) in the total raw material powder (raw material powder for garnet-type composite oxide + sintering aid). If the addition amount exceeds 1,000 ppm, there may be a risk of generating minute light absorption due to crystal defects caused by excessively contained Si. In the case of silicon oxide powder (SiO 2 powder), its primary particle size is not particularly limited, but it is preferable to use fine powder with a particle size of less than 1 μm because the sintering aid can be uniformly dispersed in the starting materials.

[0043] In the slurry obtained by the above wet mixing, the particle size distributions of terbium oxide powder, yttrium oxide powder, scandium oxide powder, and aluminum oxide powder have a single peak, the D50 value, which is the median diameter of the particle size distribution, is 400 nm or more, preferably 450 nm or more and 800 nm or less, and the D95 value, which is the value of 95% by volume cumulative 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.

[0044] As a result of intensive studies by the present inventors, as long as the particle size distribution of the slurry obtained by wet mixing exhibits a sharp single peak, the median diameter corresponding to the average particle size is preferably as large as possible, and the transparency of the paramagnetic garnet-type transparent ceramics obtained by sintering using a mixed powder of terbium oxide powder, yttrium oxide powder, scandium oxide powder, and aluminum oxide powder is improved and stabilized. Specifically, when 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 to be used is a single peak, and the D50 value, which is the median diameter, is 400 nm or more, and further the D95 value, which is the value of the cumulative 95 volume% from the minimum value side of the particle size distribution, is 2 μm or less, it becomes possible to stably and highly transparently finish the paramagnetic garnet-type transparent ceramics containing terbium and yttrium with good reproducibility.

[0045] Here, even when the D50 value is less than 400 nm, it is possible to obtain a transparent paramagnetic garnet-type oxide sintered body containing terbium and yttrium. However, its reproducibility is low, and it is affected by slight variations in conditions such as the temperature and humidity of the outside air to which the starting materials are exposed, the variation in the particle size of each powder of the starting materials to be obtained, and the variation in the amount of the sintering aid to be added, and the transparency of the paramagnetic garnet-type oxide sintered body decreases. Furthermore, when the D95 value, which is the value of the cumulative 95 volume% from the minimum value side of the particle size distribution, exceeds 2 μm, this means that the variation in the particle size of the terbium oxide powder and yttrium oxide powder, which are coarse powders, is large, and the optical quality of the paramagnetic garnet-type oxide sintered body containing terbium and yttrium using the starting materials deteriorates rapidly. Specifically, the refractive index unevenness within the optical effective surface of the obtained transparent ceramics becomes severe, and the beam quality when the transparent ceramics is transmitted as a magneto-optical material is significantly reduced.

[0046] The particle size distribution referred to here is the distribution of the abundance ratio of the particle diameters of terbium oxide powder, yttrium oxide powder, scandium oxide powder, and aluminum oxide powder, which are the starting materials not aggregated in the slurry. For example, it can be determined by obtaining a powder SEM image, measuring the particle diameter of each of a plurality (preferably 20 or more) of primary particles shown on the image data by image analysis, and calculating the average value.

[0047] In the present invention, for wet mixing, the particle size distribution of terbium oxide powder, yttrium oxide powder, scandium oxide powder, and aluminum oxide powder in the slurry obtained by mixing (the particle size distribution evaluated before drying the slurry) has a single 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 value of 95% by volume cumulative from the minimum value side of the particle size distribution, is 2 μm or less. It is preferably managed in this way. This can be achieved by mixing coarse powder terbium oxide powder and yttrium oxide powder with fine powder scandium oxide powder and aluminum oxide powder other than these, dispersing them in a dispersion medium, and pulverizing these starting materials for an extremely short time by wet mixing using a ball mill or a bead mill. That is, it is preferable to manage the mixing time of wet mixing to be as short as possible. Specifically, the mixing time is preferably 1 hour or more and 15 hours or less, and more preferably 2 hours or more and 10 hours or less.

[0048] The dispersion medium for the above wet mixing is preferably a lower alcohol having 1 to 3 carbon atoms, and more preferably ethanol.

[0049] Note that the particle size distribution here refers to that of the slurry without the binder, and only the dispersant among the organic additives finally added to the slurry may be added (the dispersant may not be added), but it is preferably about the slurry without other organic additives added. Generally, various organic additives such as dispersants, binders, lubricants, and plasticizers are added to the slurry for producing ceramics. Among these organic additives, some are suitable for dispersing the oxide particles in the slurry (such as dispersants), and some cause the oxide particles in the slurry to aggregate all at once (such as binders). In particular, as the name indicates, the binder has the effect of strongly binding (aggregating) the oxide particles in the slurry. If the binder is added before measuring the particle size distribution, the original particle size distribution of the slurry cannot be shown, and there is a drawback that correct measurement cannot be performed, so attention is required.

[0050] One of the greatest features in the manufacturing method of the paramagnetic garnet-type transparent ceramics of the present invention is the inhomogeneity of the slurry state after mixing. Using the coarse powder of terbium oxide powder and yttrium oxide powder, and the fine powder of scandium oxide powder and aluminum oxide powder as starting materials, and controlling the mixing time of wet mixing by a ball mill or a bead mill, etc. as short as possible, as a result, the particle sizes of the terbium oxide powder and yttrium oxide powder in the slurry remain coarser than those of the scandium oxide powder and aluminum oxide powder, and the particle size is in a heterogeneous state. In this case, when the wet mixing is completed and the slurry is allowed to stand, the particles of the terbium oxide powder and yttrium oxide powder are selectively likely to settle immediately. When the particles of the terbium oxide powder and yttrium oxide powder selectively start to settle, a deposition layer is formed at the bottom of the slurry, and the particles of the scandium oxide powder and aluminum oxide powder remain uniformly dispersed throughout the slurry. Therefore, it is easy for the terbium oxide powder and yttrium oxide powder to be separated from the scandium oxide powder and aluminum oxide powder within only a few minutes after standing.

[0051] Another feature in the method for manufacturing the paramagnetic garnet-type transparent ceramics of the present invention is that, despite being a slurry having such inhomogeneous characteristics, a beautiful single-peak particle size distribution can be obtained when wet particle size distribution measurement is performed. The reason for this is not clear, but presumably, since the particle size difference (difference in particle diameter) 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, it is more stable for the fine particles to adsorb on the surface of the coarse particles of the coarse powder. And as a result of such adsorption, an apparent particle size obtained by adding plus alpha to the particle diameters of the two types of coarse particles of terbium oxide powder and yttrium oxide powder, which are coarse powders, was detected by wet particle size distribution measurement. Therefore, it is presumed that a seemingly beautiful single-peak particle size distribution is obtained.

[0052] Incidentally, since the terbium oxide powder and the yttrium oxide powder are coarse powders with sufficiently large particle diameters such that they hardly aggregate by themselves, it may be possible to prevent the occurrence of a broad particle size distribution derived from secondary aggregation and tertiary aggregation as a result. 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 terbium oxide powder and the yttrium oxide powder, which are coarse powders, tend to start sedimenting immediately. At this time, the fine powders other than the fine powders firmly adsorbed on the oxides of the coarse powders remain in the slurry without sedimenting. For this reason, despite exhibiting a seemingly beautiful single-peak particle size distribution, the slurry may be phase-separated into powders that easily sediment and powders that do not easily sediment when allowed to stand. In the present invention, it is preferable that when the above slurry is allowed to stand after wet mixing, the terbium oxide powder and / or the yttrium oxide powder sediment immediately thereafter to form a deposited layer thereof.

[0053] As described above, an organic additive may be added as a dispersant to the raw material powder (raw material powder for garnet-type composite oxide + sintering aid) in order to improve its dispersibility. Examples of the dispersant include polyoxyethylene alkyl ether-based dispersants, dodecylbenzenesulfonic acid, and polyethylene glycol-based dispersants, and there is no particular limitation. When a binder is used to improve the shape retention of molding, it is preferably added at this timing. Examples of the binder include polyvinyl alcohol-based, polyacrylic acid-based, polyvinyl acetate-based, and polyvinyl butyral-based binders, but there is no particular limitation as long as the shape retention can be maintained. In this way, a slurry (raw material powder slurry for molding) in which all of the raw material powder is uniformly mixed is obtained.

[0054] (Molding) Subsequently, molding is performed using the above-mentioned raw material powder slurry for molding so as to have a predetermined shape. The molding methods include wet molding and dry molding, but in the present invention, there is no particular limitation as long as it can be made transparent. Examples of wet molding include casting molding, centrifugal casting molding, extrusion molding, and tape molding, but there is no particular limitation as long as the desired shape can be obtained. In dry molding, granules are produced from the raw material powder slurry, and uniaxial press molding is performed using a jig so as to have a predetermined shape. Examples of the granulation method include spray drying and sieving after vibration drying, but there is no particular limitation as long as the particle diameter is 2 μm or more and 1000 μm or less. If the particle diameter is less than 2 μm, each granule will be light, and the moldability may deteriorate. If it exceeds 1000 μm, the voids between the granules after molding will be large, and there is a possibility that they will remain as coarse bubbles inside the molded body.

[0055] In the present invention, it is preferable to subject the slurry to spray drying treatment to obtain a granular raw material and use the granular raw material for molding. In this case, a normal press molding process can be suitably utilized. That is, a uniaxial press process in which a very common process of filling a mold and applying pressure from a certain direction, a cold isostatic pressing (CIP) process in which the material is hermetically stored in a deformable waterproof container and pressurized by hydrostatic pressure, or a warm isostatic pressing (WIP) process can be suitably utilized. The applied pressure may be appropriately adjusted while checking the relative density of the obtained molded body, and is not particularly limited. However, for example, if it is managed within a pressure range of about 300 MPa or less that can be handled by a commercially available CIP device or WIP device, the manufacturing cost may be suppressed. Alternatively, a hot press process, a spark plasma sintering process, a microwave heating process, etc. in which not only the molding process but also sintering is carried out at once during molding can also be suitably utilized. Furthermore, it is also possible to produce a molded body by a casting molding method instead of the press molding method.

[0056] (Debinding) In the manufacturing method of the present invention, a normal debinding process can be suitably utilized. That is, it is possible to go through a temperature-raising debinding process using a heating furnace. Also, the type of the atmosphere gas at this time is not particularly limited, and air, oxygen, hydrogen, etc. can be suitably utilized. The debinding 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.

[0057] (Sintering) In the manufacturing method of the present invention, a general sintering process can be suitably utilized. That is, a heating sintering process such as a resistance heating method or an induction heating method can be suitably utilized. The atmosphere at this time is not particularly limited, and various atmospheres such as an inert gas, an oxygen gas, a hydrogen gas, a helium gas, or sintering under reduced pressure (in a vacuum) is also possible. However, since it is preferable to finally prevent the occurrence of oxygen deficiency, more preferable atmospheres include an oxygen gas and a reduced-pressure oxygen gas atmosphere.

[0058] In the sintering process of the present invention, the sintering temperature is preferably 1440 to 1780 °C, particularly preferably 1470 to 1730 °C. When the sintering temperature is within this range, it is preferable because densification is promoted while suppressing heterogeneous precipitation.

[0059] In the sintering process of the present invention, a sintering holding time of about several hours is sufficient, but the relative density of the sintered body must be densified to at least 94% or more. Further, if it is held for 10 hours or longer to densify the relative density of the sintered body to 99% or more, the final transparency is improved, which is more preferable.

[0060] (Hot Isostatic Pressing (HIP)) In the manufacturing method of the present invention, a step of further performing a hot isostatic pressing (HIP) treatment can be provided after the sintering step.

[0061] At this time, as the type of pressurized gas medium, an inert gas such as argon or nitrogen, or Ar - O 2 can be preferably used. The pressure applied by the pressurized gas medium is preferably 50 to 300 MPa, more preferably 100 to 300 MPa. If the pressure is less than 50 MPa, the transparency improvement effect may not be obtained. If it 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 convenient and preferable that the applied pressure is 196 MPa or less, which can be processed by a commercially available HIP device.

[0062] Also, 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 oxygen deficiency generation increases, which is not preferable. Also, if the heat treatment temperature is less than 1100 °C, almost no transparency improvement effect of the sintered body can be obtained. Regarding the holding time of the heat treatment temperature, there is no particular limitation, but if it is held for too long, the risk of oxygen deficiency generation increases, which is not preferable. Typically, it is preferably set in the range of 1 to 3 hours.

[0063] Note that the heater material, heat insulating material, and processing container for HIP processing are not particularly limited, but graphite, or molybdenum (Mo), tungsten (W), platinum (Pt) can be preferably used, and yttrium oxide and gadolinium oxide can also be preferably used as the processing container. Particularly when the processing temperature is 1500°C or lower, platinum (Pt) can be used as the heater material, heat insulating material, and processing container, and the pressurized gas medium can be Ar - O 2 This is preferable because it can prevent the generation of oxygen deficiency during HIP processing. When the processing temperature exceeds 1500°C, graphite is preferable as the heater material and heat insulating material. In this case, any one of graphite, molybdenum (Mo), and tungsten (W) is selected as the processing container, and then any one of yttrium oxide and gadolinium oxide is selected as the double container inside it. Additionally, filling the container with an oxygen releasing material is preferable because it can minimize the amount of oxygen deficiency generated during HIP processing.

[0064] (Oxidation annealing) In the manufacturing method of the present invention, after HIP processing, oxygen deficiency may occur in the obtained transparent ceramic sintered body, and it may exhibit a slightly light gray appearance. In that case, it is preferable to perform oxidation annealing treatment (oxygen deficiency recovery treatment) in an oxygen atmosphere or in air at a temperature below the HIP processing temperature, typically 1000 - 1500°C. The holding time in this case is not particularly limited, but it is preferably selected to be a time sufficient for recovering oxygen deficiency and within a time that does not wastefully consume electricity by performing the treatment for an excessively long time. By this oxidation annealing treatment, even a transparent ceramic sintered body that exhibits a slightly light gray appearance in the HIP processing step can be made into a colorless and transparent paramagnetic garnet - type transparent ceramic without defect absorption.

[0065] (Optical polishing) In the manufacturing method of the present invention, it is preferable to optically polish both end faces on the axis for optical use of the paramagnetic garnet-type transparent ceramics that have undergone the above series of manufacturing processes. When the measurement wavelength λ = 633 nm, the optical surface accuracy at this time is preferably λ / 2 or less, and particularly preferably λ / 8 or less. It is also possible to further reduce the optical loss by appropriately forming an antireflection film on the optically polished surface.

[0066] As described above, it is possible to provide a paramagnetic garnet-type transparent ceramic containing terbium and yttrium. The transparent ceramic can be used as a Faraday rotator operable in the wavelength band of 0.9 μm or more and 1.1 μm or less. By manufacturing this paramagnetic garnet-type transparent ceramic with the composition under the aforementioned conditions, it is possible to ensure that the Verdet constant at a wavelength of 1064 nm is 32 rad / (T·m) or more. In addition, by reducing the concentration x of yttrium (Y) in the above formula (1), the Verdet constant can also be made 36 rad / (T·m) or more. When the Verdet constant is 36 rad / (T·m) or more, replacement with the existing material TGG single crystal can be performed without changing the component design, which is simple and preferable. Also, if the Verdet constant is 32 rad / (T·m) or more, it is preferable because, by designing and devising the outer cylinder magnet, compatibility with an isolator using a TGG single crystal can be achieved without increasing the overall outer shape of the isolator. Furthermore, this paramagnetic garnet-type transparent ceramic can be finished to have a thermal conductivity of 4.8 W / m·K or more by manufacturing it with the composition under the aforementioned conditions. The measurement of the thermal conductivity can be evaluated by the laser flash method in accordance with JIS R1611.

[0067] [Magneto-optical device] Furthermore, in the present invention, since it is assumed that paramagnetic garnet-type transparent ceramics are used as magneto-optical materials, after applying a magnetic field parallel to the optical axis of the paramagnetic garnet-type transparent ceramics, a polarizer and an analyzer are set such that their optical axes are shifted by 45 degrees from each other, and it is preferable to configure and use them as a magneto-optical device. That is, the paramagnetic garnet-type transparent ceramics manufactured in the present invention are suitable for magneto-optical device applications, and are particularly preferably used as a Faraday rotator of an optical isolator having a wavelength of 0.9 to 1.1 μm.

[0068] 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 in the present invention as an optical element. In FIG. 1, the optical isolator 100 includes a Faraday rotator 110 made of paramagnetic garnet-type transparent ceramics manufactured in the present invention, and a polarizer 120 and an analyzer 130 which are polarization materials are provided before and after the Faraday rotator 110. Further, the optical isolator 100 is preferably arranged in the order of the polarizer 120, the Faraday rotator 110, and the analyzer 130, and a magnet 140 is placed on at least one of their side surfaces.

[0069] In addition, the above optical isolator 100 can be preferably used for industrial fiber laser devices. That is, 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 unstable oscillation.

Example

[0070] Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the examples. The average particle diameter of each powder of the starting materials is the volume average particle diameter (cumulative average diameter D50 (median diameter)) measured by Microtrac (laser diffraction scattering method), and was measured by Microtrac MT3300WXII manufactured by Nikkiso Co., Ltd.

[0071] [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 ), and terbium oxide crude powder (Tb 4 O 7 ), yttrium oxide crude powder (Y 2 O 3 ) made in China via a trading company were obtained. The average particle sizes of these were 200 nm, 200 nm, and 600 nm in the above order for those made by Shin-Etsu Chemical Co., Ltd. (these are referred to as fine powders), and 4 μm for those made in China (these are referred to as crude powders). Also, aluminum oxide powder (Al 2 O 3 , average particle size 300 nm; fine powder) made by Daimyo Chemical Co., Ltd. was obtained, and furthermore, a liquid of tetraethyl orthosilicate (TEOS) made by Kishida Chemical Co., Ltd. was obtained. The purity was 99.95 mass% or more for all the powder raw materials and 99.999 mass% or more for the liquid raw material. Among the above starting materials, for the oxide powders of terbium and yttrium, crude powders were used, and the mixing ratio was adjusted so as to obtain the five final compositions shown in Table 1 (that is, so that the number of moles of terbium, yttrium, scandium, and aluminum would be the molar ratios of each composition in Table 1), weighed and mixed. Subsequently, TEOS was weighed and added so that its added amount would be the mass% in Table 1 in terms of SiO 2 conversion to prepare a composite oxide raw material for wet mixing (these are referred to as those with a combination of oxide powders of the starting materials (Tb, Y - Sc, Al) being crude powder - fine powder). Also, each oxide powder of terbium and yttrium was changed from a crude powder to a fine powder to prepare a composite oxide raw material for wet mixing with the same composition as Oxide Raw Material No. 3, and this was designated as Oxide Raw Material No. 6 (this is referred to as those with a combination of oxide powders of the starting materials (Tb, Y - Sc, Al) being fine powder - fine powder). Thus, a total of six types of composite oxide raw materials for mixing were prepared.

[0072]

Table 1

[0073] (Wet mixing) The prepared composite oxide raw materials for wet mixing were subjected to dispersion and mixing treatment (wet mixing) in an alumina ball mill apparatus in ethanol while taking care to prevent mutual mixing. At this time, the mixing time was changed at three levels of 5 hours, 10 hours, and 20 hours for each raw material, and a total of 18 types of mixed raw material slurries were prepared. In addition, for each slurry, the presence or absence of the formation of a deposited layer immediately after standing was observed after wet mixing.

[0074] Also, the particle size distribution of each of the obtained slurries was measured by the following method. (Method for measuring particle size distribution) The particle size distribution of the slurry was measured as follows using a Microtrac MT3300WXII manufactured by Nikkiso Co., Ltd. with reference to JIS Z8825-2:2013. The measurement range was selected as the wet mode of 0.021 to 2000 μm (132 channels), and the circulating solvent was ethanol. 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. The refractive index was substituted with the refractive index value when the components of the mixed composition were solid-solved in the garnet structure as a representative value. Incidentally, no special dispersant was added to ethanol, but since fine powders are less likely to aggregate in ethanol than in water, it was judged that there was no problem in measuring the particle size distribution. In addition, it was confirmed whether the measured particle size distribution state was a single peak or multiple peaks (split). The particle size distributions of the slurries for each mixing time of oxide raw materials No. 3 and No. 6 are shown in Figs. 2 and 3. In Fig. 2, the one with a mixing time of 5 hours (5 h) is Example 5, the one with 10 hours (10 h) is Example 6, and the one with 20 hours (20 h) is Comparative Example 3. In Fig. 3, the one with a mixing time of 5 hours (5 h) is Comparative Example 6, the one with 10 hours (10 h) is Comparative Example 7, and the one with 20 hours (20 h) is Comparative Example 8. For the oxide raw material No. 3 in Fig. 2, the particle size distributions of all the slurries were single peaks. For the oxide raw material No. 6 in Fig. 3, the particle size distributions at mixing times of 5 hours and 10 hours were split, and the particle size distribution at 20 hours was a single peak. Also, regarding the data obtained by measurement, the D50 value, which is the median diameter of the particle size distribution, and the D95 value, which is the value of the cumulative 95 volume% from the minimum value side of the particle size distribution, were extracted.

[0075] (Forming and debinding) Subsequently, spray drying treatment was performed on the obtained slurries to produce granular raw materials with an average particle diameter of 20 μm. For the obtained 18 types of granular raw materials, uniaxial press forming and hydrostatic press treatment at a pressure of 198 MPa were performed to obtain cylindrical CIP compacts. In addition, to confirm the manufacturing stability, 3 samples were formed under each condition. The obtained compacts were degreased in a muffle furnace under the conditions of 1000 °C for 3 hours to obtain degreased compacts. (Sintering) Subsequently, the degreased compacts were charged into a vacuum sintering furnace and treated at 1500 - 1600 °C for 3 hours to obtain a total of 18 types of sintered bodies. Note that the compacts of the combination of oxide powders of the starting materials (Tb, Y - Sc, Al) with fine powder - fine powder were treated at a lower sintering temperature, and the compacts of coarse powder - fine powder were treated at a higher sintering temperature. As a result, the sintered relative density of the samples all fell within the range of 94.5 - 98%. (HIP and oxidation annealing) Each of the obtained sintered compacts was charged into a HIP furnace made of a carbon heater and subjected to HIP treatment under the conditions of 200 MPa, 1600 °C, and 2 hours in Ar. Almost no graying (oxygen deficiency absorption) was confirmed visually for any of the obtained sintered compacts. However, as a precaution, each of the obtained ceramic sintered compacts was annealed at 1450 °C for 30 hours in an atmospheric heating furnace while performing lot control for each, to take measures to sufficiently recover the oxygen deficiency. Thus, a total of 18 types of sintered compacts, including examples and comparative examples, were prepared in three sets each. (Grinding and polishing) Subsequently, each of the obtained ceramic sintered compacts was ground and polished so as to have a rod (cylindrical) shape with a diameter of 5 mm and a length of 25 mm, and the optical both end faces of each sample were finally optically polished with an optical surface accuracy of λ / 8 (when the measurement wavelength λ = 633 nm).

[0076] For the samples of the transparent ceramics obtained as described above, the total light transmittance, forward scattering rate, and extinction ratio were measured as follows. (Method for measuring total light transmittance and forward scattering rate) The total light transmittance and the forward scattering rate were measured with reference to JIS K7105 (ISO 13468-2:1999) and JIS K7136 (ISO 14782:1999). Using a spectrophotometer V-670 manufactured by JASCO Corporation, the measurement was performed at a wavelength of 1064 nm. First, for the measurement of the total light transmittance, the light dispersed by the spectroscope without setting the work (sample) in the spectrophotometer V-670 was irradiated, and the light was received by an integrating sphere set in the apparatus in advance, and the collected light was received by a detector. The obtained illuminance was defined as I 0 Subsequently, the work was set in the apparatus, and this time the dispersed light was incident on the work, and the transmitted light was collected again by the integrating sphere and received by the detector. The obtained illuminance was defined as I and calculated by the following formula. Total light transmittance (% / 25 mm) = I / I 0 × 100 Next, the measurement of the forward scattering rate is carried out in the same measurement system as before, except that the reflector on the back surface of the integrating sphere is removed with the work set as described above. The spectrally resolved light is incident on the work again, and the transmitted light is collected by the integrating sphere again and received by the detector. The obtained illuminance represents the scattering component other than the direct transmission component, and this is denoted as I S and is obtained by the following equation. Forward scattering rate (% / 25 mm) = I S / I 0 × 100 In consideration of reproducibility and variations, three measurements were made for each of the 18 types of samples produced, and the average value was calculated to obtain the total light transmittance and the forward scattering rate value for each sample.

[0077] (Measurement method of extinction ratio) The extinction ratio as a Faraday rotator was measured with reference to JIS C5877-2:2012 as follows. The extinction ratio was measured using an in-house optical system using a light source manufactured by NKT Photonics, a collimator lens, a polarizer, a work stage, an analyzer, a power meter manufactured by Gentec, and a Ge photodetector. With the light at a wavelength of 1064 nm set to a large beam diameter of 3 mmφ, the light was transmitted through the sample. In this state, when the polarization plane of the analyzer was made to coincide with the polarization plane of the polarizer, the light intensity I 0 ’ (maximum value as the laser light intensity) was measured. Subsequently, after rotating the polarization plane of the analyzer by 90 degrees to make it orthogonal to the polarization plane of the polarizer and measuring the received light intensity I’ (minimum value as the laser light intensity) again, it was obtained by calculation based on the following equation. Extinction ratio (dB) = -10 × log 10 (I’ / I 0 ’) Note that when the beam diameter is made thicker than 3 mmφ, the beam skirt starts to be kicked at the outer periphery of the 5 mmφ diameter sample. Therefore, this beam diameter of 3 mmφ was defined as a state where light was incident on almost the entire surface of the work. Regarding the extinction ratio, three samples of each of the 18 types of samples produced were measured in the above manner, and the average value was taken as the extinction ratio of each sample. The above results are shown in Table 2.

[0078]

Table 2

[0079] From the above results, in producing the paramagnetic garnet-type transparent ceramics of the present invention, first, for the combination of oxide powders of the starting materials (Tb, Y-Sc, Al) being the group of fine powder-fine powder oxide raw material No. 6 (Comparative Examples 6 to 8), the total light transmittance of the obtained transparent ceramics was low in all cases regardless of the slurry mixing time, the forward scattering rate was large, and the optical quality was poor. Regarding the group of oxide raw material Nos. 1 to 5 where the combination of oxide powders of the starting materials (Tb, Y-Sc, Al) is coarse powder-fine powder, when the wet mixing time was 20 hours (Comparative Examples 1 to 5), the forward scattering rate of the obtained transparent ceramics was 1% or more and the extinction ratio was less than 40 dB in all cases, and the optical quality was poor. When the wet mixing time of the group of oxide raw material Nos. 1 to 5 was 10 hours or less (Examples 1 to 10), in the obtained transparent ceramics, the total light transmittance was 84% or more, the forward scattering rate was less than 1%, and the extinction ratio was 40 dB or more, and the optical quality was good.

[0080] When these examples and comparative examples are sorted from the perspective of the particle size distribution of the slurry, when the D50 value, which is the median diameter, 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 2 μm or less (Examples 1 to 10), all have good optical quality. Conversely, those with a D50 value of 350 nm or less (Comparative Examples 1 to 5, 7, 8) or a D95 value of 3 μm or more (Comparative Example 6) all have poor optical quality. That is, a combination of oxide powders of starting materials (Tb, Y-Sc, Al) is weighed as coarse powder - fine powder in a desired composition ratio and wet-mixed to prepare a slurry. When the particle size distribution of the slurry has a single peak, the D50 value is 400 nm or more, and the D95 value is 2 μm or less, high-quality optical paramagnetic garnet-type transparent ceramics can be stably produced with good yield by performing molding, sintering, and annealing treatment in a predetermined process.

[0081] [Post-treatment of Examples 1, 3, 5, 7, 9] For the samples (3 sets each) of the transparent ceramics of Examples 1, 3, 5, 7, and 9 prepared in the above manner, an antireflection film (AR coat) designed so that the central wavelength is 1064 nm was coated on both optical end faces. The Verdet constant was measured for the obtained samples of the transparent ceramics with AR coat in the following manner.

[0082] (Method for measuring Verdet constant) The Verdet constant V was determined based on the following formula. The magnitude (H) of the magnetic field applied to the sample was the value calculated by simulation from the dimensions of the above 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 (in this case, 0.025 m).) The average value of the Verdet constants of 3 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 was ensured to be 32 rad / (T·m) or more in all examples.

[0083]

Table 3

[0084] Although the present invention has been described with the above embodiments, the present invention is not limited to the embodiments, and can be changed within the scope that those skilled in the art can conceive, such as other embodiments, additions, changes, deletions, etc., and as long as the effects of the present invention are achieved in any aspect, it is included in the scope of the present invention.

Description of Reference Numerals

[0085] 100 Optical isolator 110 Faraday rotator 120 Polarizer 130 Analyzer 140 Magnet

Claims

1. Terbium oxide powder, yttrium oxide powder, scandium oxide powder, and aluminum oxide powder as starting materials, and SiO as a sintering aid 2 The raw materials are wet-mixed to form a slurry, the slurry is used for molding, and then the obtained molded body is degreased and sintered to obtain the following formula (1) (Tb 1-x-y Y x Sc y ) 3 (Al 1-z Sc z ) 5 O 12 (1) (wherein 0.0494 ≤ x ≤ 0.4, 0.001 < y < 0.004, 0.596 < 1 - x - y < 0.9496, 0.0005 < z < 0.004, and 0.0015 < y + z < 0.008.) It is a sintered body of a composite oxide represented by, and as a sintering aid, SiO 2 In a method for producing a paramagnetic garnet-type transparent ceramic that obtains a paramagnetic garnet-type transparent ceramic containing more than 0% by mass and 0.1% by mass or less of A method for manufacturing paramagnetic garnet-type transparent ceramics, characterized in that the average particle diameters of the terbium oxide powder and yttrium oxide powder of the starting materials are each 3 μm or more, the average particle diameters of the scandium oxide powder and aluminum oxide powder of the starting materials are each less 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 have a single 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 value of 95% by volume accumulated from the minimum value side of the particle size distribution, is 2 μm or less.

2. The method for manufacturing paramagnetic garnet-type transparent ceramics according to Claim 1, wherein the wet mixing is performed using a ball mill or a bead mill.

3. The method for manufacturing paramagnetic garnet-type transparent ceramics according to Claim 2, wherein the mixing time using the ball mill or the bead mill is 1 hour or more and 15 hours or less.

4. The method for manufacturing paramagnetic garnet-type transparent ceramics according to any one of Claims 1 to 3, wherein the dispersion medium for the wet mixing is a lower alcohol having 1 to 3 carbon atoms.

5. The method for manufacturing paramagnetic garnet-type transparent ceramics according to any one of Claims 1 to 4, wherein the particle size distribution is for a slurry not containing a binder.

6. The method for manufacturing paramagnetic garnet-type transparent ceramics according to any one of Claims 1 to 5, wherein when the slurry is allowed to stand after wet mixing, the terbium oxide powder and / or yttrium oxide powder settle immediately thereafter to form a deposited layer.

7. The method for manufacturing paramagnetic garnet-type transparent ceramics according to any one of Claims 1 to 6, wherein the slurry is spray-dried to obtain a granular raw material, and the granular raw material is used for molding.

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