Ferromagnetic garnet-type transparent ceramics, a method for producing the same, a mixed material thereof, a magneto-optical device using the same, and a method for producing the same

Abstract

To provide a paramagnetic garnet-type transparent ceramic that can stably suppress scattering loss to a small level even when a large ceramic having a diameter φ of 8 mm or more is produced, and a method for producing the same.SOLUTION: The present invention provides a paramagnetic garnet-type transparent ceramic containing a sintered body of composite oxide represented by the following formula (1), and having a total light transmittance of 84.1% or more and a forward scattering ratio of 0.40% or less at both optical ends, even when the diameter is 8 mm or more. (Tb1-x-yYxScy)3(Al1-zScz)5O12 (1), wherein 0.05≤x≤0.45, 0<y<0.1, 0.5<1-x-y<0.95, 0.001<z<0.15, and 0<y+z<0.2).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to paramagnetic garnet-type transparent ceramics, a method for manufacturing the same, a mixed material thereof, a magneto-optical device using the same, and a method for manufacturing the same. More specifically, the present invention relates to paramagnetic garnet-type transparent ceramics containing terbium suitable for constituting magneto-optical devices such as optical isolators, a method for manufacturing the same, a mixed material thereof, a magneto-optical device using the same, and a method for manufacturing the same.

Background Art

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

[0003] The 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 emission 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 polarized wave 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 polarized wave component of light is rotated by 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 direction opposite to the rotation of the polarization plane of the polarizer 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 a 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)). The TGG crystal is currently widely installed for standard fiber laser devices. On the other hand, the Verdet constant of the TSAG crystal is said to be about 1.3 times that of the TGG crystal, and this is also a material that would not be strange even if it were installed in a fiber laser device. 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 the TAG crystal is a decomposition melting type crystal, there is a constraint 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 the TAG crystal can only be crystal-grown in a state where they are always mixed, and the growth of high-quality and large-sized TAG crystals has not been realized.

[0006] However, recently, International Publication No. 2018 / 193848 (Patent Document 3) discloses a sintered body of a complex oxide represented by the following formula, which is a paramagnetic garnet-type transparent ceramic characterized in that the linear transmittance at a wavelength of 1064 nm with an optical path length of 15 mm is 83% or more (Tb 1-x-y Sc x Ce y ) 3 (Al 1-z Sc z ) 5 O 12 (where 0 < x < 0.08, 0 ≤ y ≤ 0.01, and 0.004 < z < 0.16.) was disclosed.

[0007] Furthermore, in Non-Patent Document 1, 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 compared to existing TGG crystals (the existing 35 dB is improved to 39.5 dB or more), and the insertion loss can also be reduced (the existing 0.05 dB is improved to 0.01 to 0.05 dB). It was disclosed that the material disclosed in this Non-Patent Document 1 can be further reduced in loss compared to the material of Patent Document 3 by substituting a part of Tb ions with Y ions, and it is a material capable of obtaining an extremely high-quality garnet-type Faraday rotator.

[0008] Subsequently, Japanese Patent Application Laid-Open No. 2019-199386 (Patent Document 4) discloses a sintered body of a composite oxide represented by the following formula, containing more than 0 mass% and 0.1 mass% or less of SiO 2 as a sintering aid, and having a linear transmittance of 83.5% or more at a wavelength of 1064 nm with an optical path length of 25 mm. Paramagnetic garnet-type transparent ceramics (Tb 1-x-y 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 - x - y < 0.95, and 0.004 < z < 0.2.) was disclosed.

[0009] The material disclosed in Patent Document 4 is a material capable of obtaining a garnet-type Faraday rotator of the same high quality as that of Non-Patent Document 1 by substituting a part of Tb ions with Y ions in the same manner as in Non-Patent Document 1.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non - Patent Documents

[0011]

Non - Patent Document 1

Non - Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0012] The paramagnetic garnet-type transparent ceramics described in Patent Document 3 have a TAG and a Verdet constant without color, and have been improved so that a linear transmittance of 83% or more is ensured even with an optical path length of 15 mm. Therefore, it can be said that it has reached almost the practical level. However, although not specified in Patent Document 3, when the present inventors actually adjusted a laser beam with a wavelength of 1064 nm to a beam diameter of 1.6 mm and then incident it on a sample reproducing the example of Patent Document 3 with an output of an incident power of 100 W, it became clear that the maximum change amount of the incident laser beam diameter due to the generation of a thermal lens exceeded 15%.

[0013] Regarding Non-Patent Document 1, when the present inventors actually adjusted a laser beam with a wavelength of 1064 nm to a beam diameter of 1.6 mm and then incident it on a sample reproducing the material described in Non-Patent Document 1 with an output of an incident power of 100 W, it became clear that the maximum change amount of the incident laser beam diameter due to the generation of a thermal lens was less than 10%. However, it was also confirmed at the same time that the material described in Non-Patent Document 1 has a very low manufacturing reproducibility, and that the scattering loss deteriorates significantly when trying to produce a large sintered body with a material diameter of 8 mmφ or more.

[0014] Furthermore, regarding Patent Document 4, when the present inventors actually adjusted a laser beam with a wavelength of 1064 nm to a beam diameter of 1.6 mm and then incident it on a sample reproducing the material described in Patent Document 4 with an output of an incident power of 100 W, the maximum change amount of the incident laser beam diameter due to the generation of a thermal lens was less than 10% as in Non-Patent Document 1. The manufacturing reproducibility of the material described in Patent Document 4 was considerably improved. However, when trying to produce a large sintered body with a material diameter of 8 mmφ or more, the ratio of obtaining a sintered body with low scattering loss remained relatively low.

[0015] Note that it is known that even when using the same material, the thermal lens becomes dramatically smaller as the material diameter increases. More specifically, Non-Patent Document 2 discloses that the thermal lens is inversely proportional to the square of the material diameter. That is, there is naturally a need for a larger diameter for fiber laser optical isolators that will increasingly have higher output in the future.

[0016] The present invention has been made in view of the above circumstances, and even when producing a large-sized paramagnetic garnet-type transparent ceramic of 8 mmφ or more with a composite oxide containing at least yttrium, terbium, and aluminum as main components and having a molar concentration of terbium equal to or higher than that of yttrium, it is possible to stably suppress scattering loss to a small level. An object of the present invention is to provide a paramagnetic garnet-type transparent ceramic, a method for manufacturing the same, a mixed material thereof, a magneto-optical device using the same, and a method for manufacturing the same.

Means for Solving the Problems

[0017] To achieve the above object, in a first aspect, the present invention provides a method for manufacturing a paramagnetic garnet-type transparent ceramic including a sintered body of a composite oxide containing terbium, yttrium, scandium, and aluminum represented by the following formula (1): (Tb 1-x-y Y x Sc y ) 3 (Al 1-z Sc z ) 5 O 12 (1) (In the formula, 0.05 ≦ x ≦ 0.45, 0 < y < 0.1, 0.5 < 1 - x - y < 0.95, 0.001 < z < 0.15, and 0 < y + z < 0.2.) This manufacturing method includes a step of obtaining a molded body using a mixed raw material of the above composite oxide with the thermal history suppressed to 950°C or lower, a step of degreasing the molded body while suppressing the temperature to 950°C or lower, a step of subjecting the degreased molded body to a vacuum sintering treatment to obtain a sintered body with a relative sintering density in the range of 93.8% or more and 97.2% or less, and a step of further densifying the sintered body by hot isostatic pressing (HIP) treatment until the relative sintering density reaches 99.9% or more.

[0018] The molar ratio of the mixed raw material of the above composite oxide, in a state where the respective oxides of terbium, yttrium, and scandium and aluminum oxide are not combined, to the powder mixed in a state where the respective oxides of terbium, yttrium, and scandium and aluminum oxide are combined into a compound in any of the monoclinic phase, perovskite phase, and garnet phase is preferably not less than the molar ratio of the powder mixed in a compound state.

[0019] The compact during the above-mentioned pressureless sintering treatment may have a diameter of 11 mmφ or more.

[0020] The manufacturing method of the present invention preferably further includes a step of re-sintering the densified sintered body for 8 hours or more at a temperature exceeding the temperature of the HIP treatment after the HIP treatment, and a step of annealing the re-sintered sintered body in an oxidizing atmosphere at a temperature of 1300 °C or more.

[0021] The above-mentioned paramagnetic garnet-type transparent ceramics may further contain SiO 2 in an amount exceeding 0% by mass and not more than 0.1% by mass.

[0022] As a second aspect, the present invention relates to the above-mentioned mixed raw material of a composite oxide for producing a paramagnetic garnet-type transparent ceramic containing a sintered body of a composite oxide containing terbium, yttrium, scandium, and aluminum represented by the following formula (1), (Tb 1-x-y Y x Sc y ) 3 (Al 1-z Sc z ) 5 O 12 (1) (In the formula, 0.05 ≦ x ≦ 0.45, 0 < y < 0.1, 0.5 < 1 - x - y < 0.95, 0.001 < z < 0.15, 0 < y + z < 0.2.) The molar ratio of the powder in which the mixed raw material is mixed in a state where the respective oxides of terbium, yttrium, and scandium and aluminum oxide are not combined is higher than the molar ratio of the powder in which the respective oxides of terbium, yttrium, and scandium and aluminum oxide are combined and mixed in a state of any compound of a monoclinic phase, a perovskite phase, and a garnet phase.

[0023] As a third aspect, the present invention provides a composite oxide containing terbium, yttrium, scandium, and aluminum represented by the following formula (1), and SiO of more than 0% by mass and 0.1% by mass or less as a sintering aid 2 A paramagnetic garnet-type transparent ceramic containing (Tb 1-x-y Y x Sc y ) 3 (Al 1-z Sc z ) 5 O 12 (1) (In the formula, 0.05 ≦ x ≦ 0.45, 0 < y < 0.1, 0.5 < 1 - x - y < 0.95, 0.001 < z < 0.15, and 0 < y + z < 0.2.) When the diameter of this paramagnetic garnet-type transparent ceramic is 8 mm or more, the total light transmittance of the optically polished optical both end faces of this paramagnetic garnet-type transparent ceramic is 84.1% or more, and the forward scattering rate is 0.40% or less.

[0024] As a fourth aspect, the present invention provides a magneto-optical device configured using the above-described paramagnetic garnet-type transparent ceramic.

[0025] The magneto-optical device of the present invention may be an optical isolator that includes the above-described paramagnetic garnet-type transparent ceramic as a Faraday rotator and includes polarization materials before and after on the optical axis of the Faraday rotator and is usable in a wavelength band of 0.9 μm or more and 1.1 μm or less.

[0026] The present invention, as a fifth aspect, is a method for manufacturing a magneto-optical device, which comprises constructing a magneto-optical device using the paramagnetic garnet-type transparent ceramics obtained by the above-described method for manufacturing paramagnetic garnet-type transparent ceramics.

Effects of the Invention

[0027] According to the present invention, even when manufacturing large-sized paramagnetic garnet-type transparent ceramics with a diameter of 8 mmφ or more by processing a predetermined mixed raw material under predetermined conditions, scattering loss can be stably suppressed to a small level. Therefore, the material diameter can be increased and the thermal lens can be dramatically reduced. Further, by using this paramagnetic garnet-type transparent ceramics, it is possible to provide magneto-optical devices such as an optical isolator applicable to a high-power laser device.

Brief Description of the Drawings

[0028]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0029] <Paramagnetic Garnet-Type Transparent Ceramics> First, an embodiment of the paramagnetic garnet-type transparent ceramics according to the present invention will be described. The paramagnetic garnet-type transparent ceramics of this embodiment include a sintered body of a composite oxide containing terbium (Tb), yttrium (Y), scandium (Sc), and aluminum (Al) represented by the following formula (1). (Tb 1-x-y Y x Sc y ) 3 (Al 1-z Sc z )O 12 (1) (where 0.05 ≦ x ≦ 0.45, 0 < y < 0.1, 0.5 < 1 - x - y < 0.95, 0.001 < z < 0.15, and 0 < y + z < 0.2.)

[0030] In this complex oxide sintered body, it is essential that the main components of the 6 - coordinate sites and 4 - coordinate sites in the garnet structure be aluminum (Al). By configuring the main components of these sites with aluminum, the bondability of the crystal can be improved, and as a result, the average value of dn / dt at 30 °C ± 10 °C at a wavelength of 1064 nm can be reduced. And by setting the ratio of the aluminum occupying the 6 - coordinate sites and 4 - coordinate sites to 1 - z (0 ≦ z < 0.15), the average value of dn / dt at 30 °C ± 10 °C at a wavelength of 1064 nm can be made 9.0×10 -6 K -1 It can be controlled as follows.

[0031] In the complex oxide sintered body of this embodiment, terbium (Tb) and yttrium (Y) are selected as the main components of the 8 - coordinate sites, and the concentration of terbium is controlled in the range of 1 - x - y (0.5 < 1 - x - y < 0.95), and the concentration of yttrium is controlled in the range of x (0.05 ≦ x ≦ 0.45). When the concentration of terbium is controlled within the above - mentioned range, the Verdet constant at a wavelength of 1064 nm can be made 30 rad / (T·m) or more. Also, when the concentration of terbium is within the above - mentioned range and the concentration of yttrium is controlled within the above - mentioned range, the average value of dn / dt at 30 °C ± 10 °C at a wavelength of 1064 nm can be made 9.0×10 -6 K -1 It can be made as follows. Note that when each of these two main components simultaneously satisfies the above - mentioned range, these two characteristics can be satisfied simultaneously.

[0032] In the complex oxide sintered body of the present embodiment, scandium (Sc) is added within the range of the aforementioned formula (1). In formula (1), first, the range of y indicating the concentration of scandium is 0 < y < 0.1, preferably 0.001 < y < 0.008, and more preferably 0.002 < y < 0.004. When y 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. Furthermore, it is possible to prevent an excessive decrease in the thermal conductivity due to the homogeneity of the sintered body and grain boundary scattering.

[0033] Also, in formula (1), the range of z indicating the concentration of scandium is 0.001 < z < 0.15, and more preferably 0.02 ≦ z < 0.004. When z 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. Furthermore, it is possible to prevent an excessive decrease in the thermal conductivity due to the homogeneity of the sintered body and grain boundary scattering.

[0034] Thus, the addition amount of scandium is such that y exceeds 0 and is less than 0.1, and z exceeds 0.001 and is less than 0.15. When scandium is added within the range of formula (1) with the lower limit value of y exceeding 0 and the lower limit value of z exceeding 0.001, it becomes possible to stably manufacture a highly transparent sintered body.

[0035] The paramagnetic garnet-type transparent ceramics of the present embodiment contain, as a main component, a sintered body of the complex oxide represented by the above formula (1). Here, "containing as a main component" means containing 90% by mass or more of the complex oxide sintered body represented by formula (1). The content of the complex oxide sintered body represented by 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.

[0036] The paramagnetic garnet-type transparent ceramics of the present embodiment preferably contain SiO 2 in an amount exceeding 0% by mass and 0.1% by mass or less as a sintering aid. SiO 2If it is contained within the above range, it is preferable because the transparency of the resulting paramagnetic garnet-type ceramics is improved to a level that can withstand practical use and is stabilized.

[0037] The paramagnetic garnet-type transparent ceramics of the present embodiment are composed of the above main components and sub-components (sintering aids), 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.

[0038] 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 parts by mass or less, and particularly preferably 0.001 parts by mass or less (substantially zero).

[0039] And, even when a large sintered body with a material diameter of 8 mmφ or more is produced, the total light transmittance of the optically polished optical both end faces of the paramagnetic garnet-type transparent ceramics of the present embodiment is 84.1% or more, and the forward scattering rate is 0.40% or less. Therefore, the scattering loss can be stably suppressed to a small value. This will be described with reference to FIG. 1.

[0040] Figure 1 is a graph showing the measurement results (mass loss) of thermogravimetry (TG) when a mixed raw material of the composite oxide represented by the above formula (1) (Composition 1 described later) was heated from room temperature to about 1100°C using a thermogravimetric differential thermal analysis (TG-DTA) apparatus. When the pressed powder of the mixed raw material of each oxide of terbium, yttrium, and scandium (collectively also referred to as "rare earth oxides") and aluminum oxide before sintering was heated from room temperature, the weight gradually decreased from the starting point in the upper left of the graph in Figure 1 where the TG was 0 mg. This is a weight loss due to the volatilization of adsorbed moisture. After that, the weight loss rate changed at 300 - 350°C, indicating that the first phase change of terbium oxide (release of oxygen accompanying a valence change) occurred. Furthermore, the weight loss rate also changed around 550°C, indicating that the second phase change of terbium oxide (release of oxygen accompanying a valence change) occurred. After that, the weight loss rate changed significantly from around 900°C, indicating that the chemical reaction between the rare earth oxide and aluminum oxide and the accompanying release of oxygen started. And it was confirmed that this chemical reaction was about half completed around 950°C and the whole amount was completed above 1100°C.

[0041] Next, after the completion of sintering, it was cooled to room temperature, but almost no weight increase was observed. From this, it can be seen that the phase change of terbium (absorption of oxygen accompanying a valence change) hardly occurs in the raw material that has once undergone a chemical reaction. The slight weight increase observed near room temperature is probably due to adsorbed moisture.

[0042] Here, basically, if the rare earth oxide and aluminum oxide, which are powder raw materials, are managed in a mixed state before performing the sintering process, the mixed raw material can be made extremely homogeneous and finished smoothly. Of course, it is also possible to prevent defects such as lumps and nodules resulting from the non-uniformity of the mixed raw material. However, if the rare earth oxide and aluminum oxide in the mixed raw material undergo a chemical reaction (for example, a monoclinic phase, perovskite phase, or garnet phase is formed), the mixed raw material containing such reaction compounds becomes significantly harder than the mixed raw material not containing such reaction compounds, and furthermore, variations in the aggregated state due to uneven progress of the chemical reaction occur, and lumps, nodules, etc. also accumulate. Also, when granulating such a mixed raw material, naturally, the hardness and variations of the granules also deteriorate. And when producing a large-sized molded body using such a non-uniform mixed raw material, it becomes impossible to prevent uneven stress transmission inside the molded body and the generation of unintended large voids.

[0043] On the other hand, if the proportion of such hard and non-uniform reaction compound in the mixed raw material is suppressed to less than half of the mixed raw material, the molded body produced using the mixed raw material is homogeneous, has less uneven stress transmission, and can also prevent the generation of unwanted large voids. The proportion (molar ratio) of such hard and non-uniform reaction compound (for example, monoclinic phase, perovskite phase, garnet phase) in the entire mixed raw material at the start of sintering must be less than half, preferably less than one-third, more preferably less than one-fourth, and particularly preferably less than one-tenth. When the proportion of the hard and non-uniform reaction compound in the entire starting mixed raw material is suppressed within the above range of proportions, even when producing a particularly large-sized molded body, it can be finished into a high-quality molded body from which a transparent sintered body with low scattering and high quality can be obtained.

[0044] The temperature at which the chemical reaction between the rare earth oxide and aluminum oxide starts can be roughly read as about 900 °C from Figure 1. Also, it can be read that about half of this chemical reaction is completed at 950 °C. Further, as shown in Figure 1, the raw materials that have once undergone the chemical reaction cannot return to the original unreacted state even when cooled. Therefore, for the production of the molded body, by using mixed raw materials with a heat history suppressed to 950 °C or lower, the molar ratio of the powder in the unreacted state of the rare earth oxide and aluminum oxide in the mixed raw materials during the production of the molded body can be made equal to or higher than the molar ratio of the powder in the state of any of the compounds of the monoclinic phase, perovskite phase, and garnet phase in which the rare earth oxide and aluminum oxide have reacted. For example, before producing the molded body, when the mixed material is calcined or heat-dried, in order to suppress the heat history to 950 °C or lower, it is necessary to set the temperature to 950 °C or lower. The heat history is preferably suppressed to 920 °C or lower, and more preferably suppressed to 900 °C or lower.

[0045] Also, for the paramagnetic garnet-type transparent ceramics of the present embodiment, when a degreasing treatment is performed to burn out and remove an organic binder or the like after the production of the molded body, it is preferable that the degreasing treatment temperature is suppressed to 950 °C or lower, and more preferably suppressed to 920 °C or lower. When the degreasing treatment temperature of the molded body is controlled within this range, unintentional thermal shrinkage in an atmosphere that is not a reduced-pressure environment due to heating of the degreased body can be prevented.

[0046] Furthermore, the paramagnetic garnet-type transparent ceramics of the present embodiment are sintered in a reduced-pressure atmosphere. When sintering is performed in a reduced-pressure atmosphere, oxygen gas that desorbs in large quantities when Tb in the tetravalent state changes to the trivalent state due to heating can be efficiently discharged and volatilized outside the sintered body. Also, when sintering is performed in a reduced-pressure atmosphere, the relative sintered density of the obtained sintered body is set in the range of 93.8% or more and 97.2% or less. When the relative sintered density of the obtained sintered body is controlled within this range, the residual air bubbles inside the sintered body can be made into closed pores, while the sintered particle size can be controlled without being made excessively large. It is more preferable that the relative sintered density of the sintered body obtained by sintering in a reduced-pressure atmosphere is in the range of 93.8% or more and 96.5% or less.

[0047] Then, the paramagnetic garnet-type transparent ceramics of the present embodiment are further subjected to hot isostatic pressing (HIP) treatment on the sintered body within the above sintering density range until the relative sintering density of the sintered body reaches 99.9% or more, thereby densifying it. By doing so, it becomes possible to effectively perform HIP treatment in a state where the sintered particle size is small. Therefore, even for a large sintered body with a diameter of 8 mmφ or more, densification proceeds sufficiently up to the center part thereof.

[0048] The paramagnetic garnet-type transparent ceramics of the present embodiment obtained by such heat history management and various treatments can have a total light transmittance of 84.1% or more and a forward scattering rate of 0.40% or less for the optically polished optical both end faces, even if the outer diameter is as large as 8 mmφ or more. Further, the paramagnetic garnet-type transparent ceramics of the present embodiment may be processed so that its length becomes 17 mm or more for use as a target magneto-optical material. When the length of the paramagnetic garnet-type transparent ceramics is 17 mm or more, it is preferable because incident light in the wavelength band of 0.9 μm or more and 1.1 μm or less can be rotated by 45 degrees regardless of the configuration and size of the magnet to be externally mounted.

[0049] In addition, it is preferable that the paramagnetic garnet-type transparent ceramics of the present embodiment are further subjected to a re-sintering treatment at a temperature exceeding the HIP treatment temperature for 8 hours or more after the HIP treatment. Thereby, internal strain and residual bubbles can be removed. The re-sintering treatment time is preferably 8 hours or more, and more preferably 10 hours or more. By making the re-sintering treatment time sufficiently long in this way, even for a large sintered body with a diameter of 8 mmφ or more, residual strain and residual bubbles can be sufficiently eliminated up to the center part thereof.

[0050] In addition, for the paramagnetic garnet-type transparent ceramics of the embodiment, after the sintering treatment, it is preferable to further anneal the obtained sintered body in an oxidizing atmosphere at 1300°C or higher. Thereby, oxygen deficiency can be eliminated. The annealing time at this time is preferably 8 hours or more, more preferably 20 hours or more, and particularly preferably 30 hours or more. By making the annealing time sufficiently long in this way, even for a large-sized sintered body with a diameter of 8 mmφ or more, oxygen deficiency can be sufficiently recovered up to the central part thereof.

[0051] <Method for manufacturing paramagnetic garnet-type transparent ceramics> Next, an embodiment of a method for manufacturing the paramagnetic garnet-type transparent ceramics according to the present invention will be described. In this embodiment, a molding step of obtaining a molded body using a mixed raw material of a composite oxide represented by the above formula (1) in which the thermal history is suppressed to 950°C or lower, a debinding step of debinding the molded body while suppressing the temperature to 950°C or lower, a sintering step of subjecting the debound molded body to a pressureless sintering treatment to obtain a sintered body having a relative sintered density in the range of 93.8% or more and 97.2% or less, and a step of further densifying the sintered body by hot isostatic pressing (HIP) treatment until the relative sintered density becomes 99.9% or more are mainly included. Hereinafter, the mixed raw material used and each step will be described.

[0052] (1. Mixed raw material) As the raw materials used in this embodiment, it is preferable to use powders of oxides of terbium, yttrium, scandium, and aluminum. The purity of the raw materials at this time is preferably 99.9% by mass or more, and particularly preferably 99.99% by mass or more. Then, each raw material is weighed in a predetermined amount so as to have the composition of the composite oxide represented by the above formula (1) and mixed to obtain a mixed raw material.

[0053] In this mixed raw material, silicon oxide (SiO 2 ) may be added in an amount of more than 0% by mass and 0.1% by mass or less as a sintering aid. The mixed raw material is appropriately treated by a wet ball mill, a bead mill, or a jet mill.

[0054] In addition, various organic additives may be added to this mixed raw material for the purpose of improving the quality stability and yield in the manufacturing process of the sintered body of the composite oxide. In the present embodiment, these are not particularly limited, and 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 inhibit the control of the properties (such as particle size distribution) of the raw material to be manufactured.

[0055] Then, as this mixed raw material, one with a thermal history suppressed to 950°C or lower is used. By suppressing the thermal history to 950°C or lower, the molar ratio of the powder mixed in a state where the rare earth oxide and aluminum oxide in the mixed raw material are not combined is equal to or higher than the molar ratio of the powder mixed in the state of any of the compounds of the monoclinic phase, perovskite phase, and garnet phase in which the rare earth oxide and aluminum oxide are combined.

[0056] (2. Forming step) In the manufacturing method of the present embodiment, a normal press forming process can be preferably used. That is, a very general uniaxial press process of filling a mold and applying pressure from a certain direction, a cold isostatic pressing (CIP) process of hermetically storing in a deformable waterproof container and applying pressure with hydrostatic pressure, or a warm isostatic pressing (WIP) process can be preferably used. The applied pressure may be appropriately adjusted while checking the relative density of the obtained molded body (compressed powder), and there is no particular limitation. 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., which not only perform the forming process but also sinter all at once during forming, can also be preferably used. Also, instead of the press forming method, a molded body can be produced by preparing a wet slurry from the above mixed raw materials and using a casting forming method. Forming methods such as pressure casting, centrifugal casting, and extrusion molding can also be adopted by optimizing the combination of the shape and size of the oxide powder as the starting material and various organic additives.

[0057] In the manufacturing method of the present embodiment, in order to make the outer diameter of the obtained paramagnetic garnet-type transparent ceramics 8 mmφ or more after outer peripheral grinding, it is preferable to produce by using a large-diameter jig with an inner diameter of the uniaxial press forming jig of 11 mmφ or more. The upper limit value of the jig inner diameter is not particularly limited, but it may be, for example, 150 mmφ or less.

[0058] (3. Debinding process) In the manufacturing method of this embodiment, a normal degreasing process can be preferably used. For example, it is possible to go through a temperature-raising degreasing 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 preferably used. Regarding the degreasing temperature, it is set to be equal to or higher than the temperature at which the organic components of the added organic additives can be sufficiently decomposed and removed, and is suppressed to 950 °C or lower, and a range suppressed to 920 °C or lower is more preferable. By controlling the degreasing treatment temperature within such a range, it is possible to prevent the degreased compact from undergoing unintended thermal shrinkage in an atmosphere that is not a reduced-pressure environment due to heating.

[0059] (4. Sintering process) In the manufacturing method of this embodiment, a general sintering process can be preferably used. For example, a heating sintering process such as a resistance heating method or an induction heating method can be preferably used. Also, the atmosphere at this time is set to a reduced-pressure environment (in vacuum). By performing such a reduced-pressure sintering treatment, even for a large sintered body with a diameter of 8 mmφ or more, the deoxidized gas detached from the degreased compact can be sufficiently discharged to the outside of the system up to the central part. The degree of vacuum is, for example, 1×10 -3 torr or less is preferable.

[0060] The sintering temperature in the sintering process of this embodiment is preferably 1400 to 1780 °C, and particularly preferably 1500 to 1750 °C. When the sintering temperature is within this range, it is preferable because densification is promoted while suppressing heterogeneous precipitation.

[0061] The sintering holding time in the sintering process of this embodiment is sufficient at about several hours, but it is controlled so that the relative density of the sintered body is in the range of 93.8% or more and 97.2% or less. The control of the sintering process to obtain such a sintering density can be carried out by repeating several preliminary experiments.

[0062] (5. HIP treatment process) In the manufacturing method of this embodiment, after going through the sintering process, a hot isostatic pressing (HIP) treatment is further performed. The type of the pressurized gas medium used for the HIP treatment is an inert gas such as argon or nitrogen, or Ar - O 2It 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 effect of improving transparency may not be obtained. If it exceeds 300 MPa, no further improvement in transparency can be obtained even if the pressure is increased, and the load on the device may be 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 processing device.

[0063] Also, the temperature of the HIP treatment (predetermined holding temperature) 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 effect of improving the transparency of the sintered body can be obtained. The holding time of the heat treatment temperature is not particularly limited, 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.

[0064] In addition, the heater material, heat insulating material, and processing container used for the HIP treatment are not particularly limited, but graphite, or molybdenum (Mo), tungsten (W), platinum (Pt) can be preferably used. As the processing container, yttrium oxide and gadolinium oxide can also be preferably used. 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 Since it can be set as such, it is preferable because it can prevent the generation of oxygen deficiency during the HIP treatment. 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 further, any one of yttrium oxide and gadolinium oxide is selected as a double container inside it, and an oxygen releasing material is filled in the container. Then, it is preferable because the amount of oxygen deficiency generated during the HIP treatment can be suppressed to be as small as possible.

[0065] (6. Re - sintering process) In the manufacturing method of this embodiment, after HIP treatment, it may be further sintered at a temperature exceeding the HIP treatment temperature for 8 hours or more. Thereby, internal strain and residual bubbles can be removed. In particular, when manufacturing a large sintered body using a large-diameter jig with an inner diameter of the uniaxial press molding jig of 11 mmφ or more, residual strain and residual bubbles can be sufficiently eliminated up to the center part thereof, and a higher-quality product can be manufactured with good reproducibility. Note that the upper limit temperature of the resintering is preferably 1780°C or lower. If it exceeds 1780°C, the risk of oxygen deficiency generation increases, which is not preferable. The resintering treatment time is preferably set longer as the diameter of the sintered body to be treated is thicker, and more preferably 10 hours or more.

[0066] (7. Annealing process) In the manufacturing method of this embodiment, after finishing the resintering treatment, for the purpose of recovering oxygen deficiency in the obtained transparent ceramics, it is preferable to perform annealing treatment in an oxygen atmosphere of 1300°C or higher. Thereby, even for a large sintered body with a diameter of 8 mm or more, a colorless and transparent paramagnetic garnet-type transparent ceramic without defect absorption can be obtained. The upper limit temperature of the annealing treatment is typically preferably 1500°C or lower.

[0067] (8. Optical polishing) In the manufacturing method of this embodiment, for the paramagnetic garnet-type transparent ceramic that has undergone the above series of manufacturing processes, it is preferable to optically polish both end faces on the axis to be optically used. At this time, the optical surface accuracy is preferably λ / 2 or less, and particularly preferably λ / 8 or less when the measurement wavelength λ = 633 nm. Note that it is also possible to further reduce the optical loss by appropriately forming an antireflection film on the optically polished surface.

[0068] In addition, in the manufacturing method of the present embodiment, it is preferable to perform outer peripheral polishing on the obtained paramagnetic garnet-type transparent ceramics to obtain a large sintered body with a diameter of 8 mm or more. The upper limit value of the diameter is not particularly limited, but for example, it may be 150 mm or less. Further, since the obtained paramagnetic garnet-type transparent ceramics are used as a magneto-optical material, they may be processed so that their length becomes 17 mm or more. By setting the length of the paramagnetic garnet-type transparent ceramics to 17 mm or more, it is possible to rotate incident light in the wavelength band of 0.9 μm or more and 1.1 μm or less by 45 degrees regardless of the configuration and size of the magnet to be externally mounted, which is preferable.

[0069] As described above, a sintered body of a composite oxide containing terbium, yttrium, scandium, and aluminum represented by the above formula (1) is included, and even if the diameter is 8 mmφ or more, the total light transmittance of the optically polished optical both end faces is 84.1% or more, and the forward scattering rate is 0.40% or less. A paramagnetic garnet-type transparent ceramic can be obtained. This paramagnetic garnet-type 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.

[0070] <Magneto-optical device> Furthermore, an embodiment of the magneto-optical device according to the present invention will be described. The magneto-optical device according to the present invention is configured using the above-described paramagnetic garnet-type transparent ceramics. The above-described paramagnetic garnet-type transparent ceramics can be used as a magneto-optical material. Specifically, after applying a magnetic field parallel to the optical axis to this paramagnetic garnet-type transparent ceramics, it is preferable to configure and use a magneto-optical device by setting a polarizer and an analyzer such that their optical axes are shifted by 45 degrees from each other. In particular, the paramagnetic garnet-type transparent ceramics according to the present invention are suitably used as a Faraday rotator of an optical isolator having a wavelength of 0.9 to 1.1 μm as a magneto-optical device.

[0071] FIG. 2 is a cross-sectional view schematically showing an example of an optical isolator which is a magneto-optical device including a Faraday rotor made of the paramagnetic garnet type transparent ceramics of the present invention as an optical element. As shown in FIG. 2, the optical isolator 100 includes, inside its housing 102, a Faraday rotor 110 made of the above-described paramagnetic garnet type transparent ceramics, a polarizer 120 made of a polarization material, and an analyzer 130. These are arranged in the order of the polarizer 120, the Faraday rotor 110, and the analyzer 130 along the optical axis 104 of the Faraday rotor. The polarization vibration plane of the polarizer 120 and the polarization vibration plane of the analyzer 130 are arranged so that the relative angle is 45°. Further, the optical isolator 100 includes a magnet 140 for applying a magnetic field to the Faraday rotor 110 around the Faraday rotor 110 in the housing 102.

[0072] Such an optical isolator 100 can be suitably used for an industrial fiber laser device (not shown). The optical isolator can prevent the reflected light of the laser light emitted from the laser light source from returning to the light source and causing unstable oscillation.

Examples

[0073] 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. [Examples 1 to 7, Comparative Examples 1 to 7] Terbium oxide powder, yttrium oxide powder, scandium oxide powder manufactured by Shin-Etsu Chemical Co., Ltd., and aluminum oxide powder manufactured by Dainippon Chemical Co., Ltd. were obtained. Further, tetraethyl orthosilicate (TEOS) liquid manufactured by Kishida Chemical Co., Ltd. was obtained. The purity of the powder raw materials was 99.95% by mass or more, and the purity of the liquid raw material was 99.999% by mass or more. Then, using the above raw materials, the mixing ratio was adjusted to prepare mixed raw materials having two final compositions, Composition 1 and Composition 2 shown in Table 1. As a method for adjusting the mixing ratio, each oxide powder was weighed and mixed so that the number of moles of terbium, yttrium, aluminum, and scandium was the molar ratio of each composition in Table 1. Subsequently, TEOS was added so that the added amount was SiO 2Weighed to achieve the mass percentages in Table 1 by conversion and added to the mixed raw materials.

[0074]

Table 1

[0075] Then, while taking care to prevent mutual mixing, they were dispersed and mixed in an alumina ball mill apparatus in ethanol. The treatment time was set to 15 hours. After that, spray drying treatment was carried out to produce granular raw materials with an average particle size of 20 μm for all. For the two types of obtained granular raw materials, using seven types of uniaxial press molding jigs with different inner diameters, ten molded bodies shown in Table 2 were produced for each. The length was adjusted by the raw material filling amount so that the molded body length became 33 mm for all. Then, all the molded bodies were subjected to hydrostatic pressure pressing treatment at a pressure of 198 MPa to obtain CIP molded bodies. All the obtained molded bodies were degreased in a muffle furnace under the conditions of 800 °C for 3 hours to obtain degreased molded bodies.

[0076]

Table 2

[0077] Subsequently, all the above degreased molded bodies were divided into five pieces each. One group was adjusted to a sintering temperature of 1510 - 1570 °C in a vacuum sintering furnace and treated for 3 hours to obtain sintered bodies with a sintered density of 97.2% or less. Furthermore, the remaining five degreased molded bodies each were adjusted to a sintering temperature of 1580 - 1640 °C in the same vacuum sintering furnace and treated for 3 hours to obtain sintered bodies with a sintered density of 98% or more. The sintered densities of each sample group at this time were summarized in Table 3.

[0078]

Table 3

[0079] 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 3 hours in Ar. All of the obtained sintered compacts had a relative density of 99.9% or more. Also, their appearance showed a bluish-gray color (oxygen deficiency absorption).

[0080] Thereafter, in order to eliminate residual bubbles over the entire region including the center part of the sintered compact, all of the HIP-treated sintered compacts were subjected to a re-sintering treatment in a vacuum sintering furnace at a sintering temperature of 1730 °C for 15 hours.

[0081] Subsequently, for each of the obtained ceramics, while managing each lot (example number, comparative example number), an annealing treatment was performed at 1400 °C for 30 hours in an atmospheric heating furnace to perform a treatment for sufficiently recovering oxygen deficiency. In this way, a total of 28 types of sintered compact sets, 5 each for the examples and comparative examples, were prepared. Also, the outer diameter of each ceramic at this point was measured. The results are also summarized in Table 3.

[0082] Thereafter, for each of the obtained ceramics, the outer diameter was adjusted as follows by centerless outer peripheral grinding. That is, for Examples 1, 8, Comparative Examples 1, 8, it was made 4.2 mm in diameter, for Examples 2, 9, Comparative Examples 2, 9, it was made 5.8 mm in diameter, for Examples 3, 10, Comparative Examples 3, 10, it was made 7.3 mm in diameter, for Examples 4, 11, Comparative Examples 4, 11, it was made 8.7 mm in diameter, for Examples 5, 12, Comparative Examples 5, 12, it was made 11.1 mm in diameter, for Examples 6, 13, Comparative Examples 6, 13, it was made 22.4 mm in diameter, and for Examples 7, 14, Comparative Examples 7, 14, it was centerless processed to 8.1 mm in diameter. Note that generally, the outer diameter of a sintered compact is known to vary in the finished size reflecting the variation in the degree of shrinkage. Therefore, in order to be mounted on an optical device such as a fiber laser processing machine, it is preferable that the outer diameter is processed and aligned with high precision.

[0083] After that, they were all cut and polished to a length of 23 mm, and precision mirror polishing was performed so that the optical both end faces of each sample had an optical surface accuracy of λ / 8 (when the measurement wavelength λ = 633 nm). Note that even if the lengths are the same, it is known that the applied magnetic field required for the incident light to rotate by 45 degrees increases as the outer shape becomes larger. Although detailed description is omitted in this specification, in order to function as an actual Faraday rotator, it is essential to appropriately adjust the material and thickness of the outer cylinder magnet, the magnetic field application pattern, etc. according to the outer diameter of each sintered body.

[0084] Regarding each of the ceramics of the examples and comparative examples obtained as described above, the total light transmittance, forward scattering ratio, and extinction ratio were measured as follows, respectively.

[0085] (Measurement method of total light transmittance and forward scattering ratio) The total light transmittance and forward scattering ratio 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 this light was received by the integrating sphere pre-set in the apparatus, and the collected light was received by the detector. The obtained illuminance was designated 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 designated as I, and the total light transmittance was obtained by the following formula. Total light transmittance (% / 25 mm) = I / I 0 ×100

[0086] Next, for the measurement of the forward scattering ratio, in the same measurement system as above except that the reflector on the back surface of the integrating sphere was removed with the work set, the dispersed light was incident on the work again, and the transmitted light was collected again by the integrating sphere and received by the detector. The obtained illuminance represents the scattering component other than the direct transmission component, and this was designated as I S and the forward scattering ratio was obtained by the following formula. Forward scattering rate (% / 25 mm) = I S / I 0 ×100

[0087] In consideration of the influence of reproducibility and variation, five measurements were made for each condition, and the average value was calculated and used as the total light transmittance and forward scattering rate values for each example and comparative example. Note that a beam diameter of 2 mmφ was used regardless of the diameter of the sintered body, and the incident position was adjusted to be approximately at the center of the optically effective surface.

[0088] (Measurement method of extinction ratio) The extinction ratio as a Faraday rotator was measured as follows. The extinction ratio was measured using a light source manufactured by NKT Photonics, and an in-house optical system using a collimator lens, a polarizer, a work stage, an analyzer, a power meter manufactured by Gentec, and a Ge photodetector. Light with a wavelength of 1064 nm was adjusted by the collimator lens to a beam diameter of 1.5 mmφ and transmitted through the sample. In this state, the intensity of light I 0 ’(maximum value as the laser light intensity) was measured. Subsequently, the polarization plane of the analyzer was rotated by 90 degrees to be orthogonal to the polarization plane of the polarizer, and the received light intensity I’ (minimum value as the laser light intensity) was measured again. Then, the extinction ratio was obtained by calculation based on the following formula. Extinction ratio (dB) = -10 × log 10 (I’ / I 0 ’)

[0089] The measurement results of the total light transmittance, forward scattering rate, and extinction ratio are summarized in Table 4.

[0090]

Table 4

[0091] From the results in Table 4, in the production of the composite oxide sintered body of the present invention, for the group of examples adjusted so that the sintering density in the sintering process was in the range of 93.9% to 97.1%, for all sintered bodies with a diameter after centerless grinding from 4.2 mm to 22.4 mm, extremely low-scattering sintered bodies with a total light transmittance of 84.1% or more and a forward scattering rate of 0.4% or less could be produced without depending on the outer diameter dimension. Also, all the extinction ratios were 42 dB or more.

[0092] On the other hand, in the group of comparative examples where the sintering density in the sintering process was 98% or more, in the case of relatively thin sintered bodies with a diameter after centerless grinding of 7.3 mm or less, low-scattering and high-quality sintered bodies with a total light transmittance of 84% or more and a forward scattering rate of 0.4% or less were obtained. However, when the diameter after centerless grinding became 8.1 mm or more and larger, the total light transmittance also deteriorated to less than 84% in proportion to the outer diameter size, and the forward scattering rate also deteriorated to 0.45% or more, and it was confirmed that the scattering of the sintered body increased.

[0093] From the comprehensive results of the present examples and comparative examples, the following can be concluded. That is, when producing a thin sintered body with a diameter of 8 mm or less, it is not necessary to control the sintering density before the HIP treatment within a certain range. On the other hand, when trying to produce a thick sintered body with a diameter of 8 mm or more, it is necessary to strictly control the sintering density at the stage before the HIP treatment within the range of 93.8% or more and 97.2% or less. When the sintering density is 93.7% or less, a part of the residual pores inside the sintered body remains as open pores, and these open pores become voids due to the fact that they cannot be crushed by the HIP treatment, so it becomes impossible to increase the sintering density of the sintered body to 99.9% in the HIP process.

[0094] Thus, by strictly controlling the sintering density at the stage before the HIP process within the range of 93.8% or more and 97.2% or less, the sintered body of the composite oxide can be finished with low scattering without problems even if its molding size, particularly the outer diameter size, is 8 mmφ or more. Therefore, it becomes possible to produce a composite oxide sintered body mountable on a high-power laser system with high quality and good reproducibility. In fact, by mounting the sintered body on a high-power laser system, it becomes possible to provide a high-quality high-power laser system in which the beam profile does not collapse even when a high-power laser is emitted.

[0095] Although the present invention has been described so far with the above-described embodiments, the present invention is not limited to these embodiments and can be changed within the scope that those skilled in the art can conceive, such as other embodiments, additions, changes, deletions, etc. As long as the effects of the present invention are exhibited in any aspect, it is included in the scope of the present invention.

Explanation of Reference Numerals

[0096] 100 Optical isolator 110 Faraday rotator 120 Polarizer 130 Analyzer 140 Magnet

Claims

1. A method for manufacturing a paramagnetic garnet-type transparent ceramic including a sintered body of a composite oxide containing terbium, yttrium, scandium, and aluminum represented by the following formula (1), (Tb １-ｘ-ｙ Y ｘ Sc ｙ ) ３ (Al １－ｚ Sc ｚ ) ５ O １２ (1) (wherein 0.05 ≦ x ≦ 0.45, 0 < y < 0.1, 0.5 < 1 - x - y < 0.95, 0.001 < z < 0.15, 0 < y + z < 0.2). A step of obtaining a molded body using a mixed raw material of the composite oxide with the thermal history suppressed to 950 °C or lower, A step of degreasing the molded body while suppressing the temperature to 950 °C or lower, A step of subjecting the degreased molded body to a vacuum sintering treatment to obtain a sintered body having a relative sintered density in the range of 93.8% or more and 97.2% or less, A step of further densifying the sintered body by hot isostatic pressing (HIP) treatment until the relative sintered density becomes 99.9% or more A method for manufacturing a paramagnetic garnet-type transparent ceramic including the above steps.

2. In the mixed raw material of the composite oxide, the molar ratio of the powder in which the respective oxides of terbium, yttrium, and scandium and aluminum oxide are mixed in a state where they are not combined is included in an amount equal to or more than the molar ratio of the powder in which the respective oxides of terbium, yttrium, and scandium and aluminum oxide are combined and mixed in a state of any compound of a monoclinic phase, a perovskite phase, and a garnet phase. The method for manufacturing a paramagnetic garnet-type transparent ceramic according to Claim 1.

3. The method for manufacturing a paramagnetic garnet-type transparent ceramic according to Claim 1 or 2, wherein the molded body during the vacuum sintering treatment has a diameter of 11 mmφ or more.

4. A step of re-sintering the densified sintered body at a temperature exceeding the temperature of the HIP treatment for 8 hours or more after the HIP treatment, A step of further annealing the re-sintered sintered body in an oxidizing atmosphere at a temperature of 1300 °C or higher The method for manufacturing a paramagnetic garnet-type transparent ceramic according to Claim 1 or 2, further including the above steps.

5. The above-mentioned paramagnetic garnet-type transparent ceramics further contain SiO ２ in an amount of more than 0% by mass and 0.1% by mass or less as a sintering aid, according to the method for producing a paramagnetic garnet-type transparent ceramics according to claim 1 or 2.

6. A mixed raw material of the composite oxide for manufacturing a paramagnetic garnet-type transparent ceramic including a sintered body of a composite oxide containing terbium, yttrium, scandium, and aluminum represented by the following formula (1), (Tb １-ｘ-ｙ Y ｘ Sc ｙ ) ３ (Al １－ｚ Sc ｚ ) ５ O １２ (1) (wherein 0.05 ≦ x ≦ 0.45, 0 < y < 0.1, 0.5 < 1 - x - y < 0.95, 0.001 < z < 0.15, 0 < y + z < 0.2). The above mixed raw material is a mixed raw material in which the molar ratio of the powder mixed in a state where the oxides of terbium, yttrium, and scandium and aluminum oxide are not combined is not less than the molar ratio of the powder mixed in a state where the oxides of terbium, yttrium, and scandium and aluminum oxide are combined to form a compound in any of the monoclinic phase, perovskite phase, and garnet phase. The above mixed raw material includes a powder mixed in a state where the oxides of terbium, yttrium, and scandium and aluminum oxide are not combined, and a powder mixed in a state where the oxides of terbium, yttrium, and scandium and aluminum oxide are combined to form a compound in any of the monoclinic phase, perovskite phase, and garnet phase. The mixed raw material in which the powder mixed in a state where the compound is in any of the monoclinic phase, perovskite phase, and garnet phase is less than half in molar ratio with respect to the whole of the above mixed raw material.

7. A complex oxide containing terbium, yttrium, scandium, and aluminum represented by the following formula (1), and SiO in an amount of more than 0% by mass and 0.1% by mass or less as a sintering aid ２ which is a paramagnetic garnet-type transparent ceramic containing (Tb １-ｘ-ｙ Y ｘ Sc ｙ ) ３ (Al １－ｚ Sc ｚ ) ５ O １２ (1) (wherein 0.05 ≦ x ≦ 0.45, 0 < y < 0.1, 0.5 < 1 - x - y < 0.95, 0.001 < z < 0.15, 0 < y + z < 0.2). A paramagnetic garnet-type transparent ceramic in which when the diameter of the paramagnetic garnet-type transparent ceramic is 8 mm or more, the total light transmittance of the optically polished optical both end faces of the paramagnetic garnet-type transparent ceramic is 84.1% or more and the forward scattering rate is 0.40% or less.

8. A magneto-optical device constituted by using the paramagnetic garnet-type transparent ceramic according to Claim 7.

9. The magneto-optical device according to Claim 8, which is an optical isolator that includes the above paramagnetic garnet-type transparent ceramic as a Faraday rotator and has polarizing materials provided before and after on the optical axis of the Faraday rotator and is usable in a wavelength band of 0.9 μm or more and 1.1 μm or less.

10. A method for manufacturing a magneto-optical device that constitutes a magneto-optical device by using the paramagnetic garnet-type transparent ceramic obtained by the method for manufacturing the paramagnetic garnet-type transparent ceramic according to Claim 1 or 2.

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