Terbium-containing paramagnetic garnet-type transparent ceramic, method for producing same, raw material mixture thereof, magneto-optical device using same, and method for producing same

Abstract

Provided are: a terbium-containing paramagnetic garnet-type transparent ceramic having the following properties: when a laser beam having a wavelength of 1064 nm and a beam diameter of 1.6 mm is irradiated thereon at an incident power even increased to 160 W, the maximum change in the diameter of the incident laser beam can be maintained at 10% or less; and others. The terbium-containing paramagnetic garnet-type transparent ceramic includes a sintered body of a composite oxide represented by formula (1) and has a total light transmittance of 84.8% or more at a wavelength of 600 nm. (1) (Tb1-x-yYxScy) 3 (Al1-zScz) 5O12 (wherein, in the formula, x is greater than or equal to 0.35 and less than or equal to 0.45, 0 lt; y < lt >; 0.03 to 0.5 lt; 1-x-y < lt >; 0.65, 0.001 lt, 0.65, 0.01 lt; z < lt >; 0.03, and 0 lt; y + z < lt >; 0.06) of the method. The magneto-optical element according to the invention is an optical isolator equipped with the transparent ceramic as a Faraday rotator 110, and also equipped with a polarizer 120 and an analyzer 130 on the optical axis 102 of the Faraday rotator on the front side and the rear side, respectively, of the Faraday rotator, and can be used in the wavelength band of 0.9-1.1 [mu] m.

Description

TECHNICAL FIELD

[0001] The present invention relates to a terbium-containing paramagnetic garnet-type transparent ceramic, a production method thereof, a raw material mixture thereof, and a magneto-optical device using the same and a production method of the magneto-optical device, and more particularly, to a terbium-containing paramagnetic garnet-type transparent ceramic suitable for constituting a magneto-optical device such as an optical isolator, a production method thereof, a raw material mixture thereof, and a magneto-optical device using the same and a production method of the magneto-optical device. BACKGROUND

[0002] In recent years, a laser processing machine using a fiber laser has become very popular because it has been able to increase output. In addition, among laser sources included in a laser processing machine, in a case where light from the outside is incident thereon, a phenomenon in which a resonant state becomes unstable and an oscillation state is disturbed occurs. In particular, in a case where oscillation light is reflected by an intermediate optical system and returns to a light source, the oscillation state is significantly disturbed. In order to prevent the disturbance, an optical isolator is generally provided, for example, in front of the light source.

[0003] The optical isolator includes a Faraday rotator, a polarizer disposed on a light incident side of the Faraday rotator, and an analyzer disposed on a light exit side of the Faraday rotator. In addition, the Faraday rotator is used by applying a magnetic field parallel to a traveling direction of light. In this case, regardless of whether the light moves forward or backward in the Faraday rotator, a polarization line segment of the light is rotated only in a certain direction. In addition, the Faraday rotator is adjusted to have a length such that the polarization line segment of the light is rotated only by 45 degrees. Here, when the polarization planes of the polarizer and the analyzer are deviated by 45 degrees in a rotation direction of the forward traveling light, the polarization of the forward traveling light is transmitted due to the polarization coinciding with a position of the polarizer and a position of the analyzer. In addition, the polarization of the backward traveling light is rotated by 45 degrees in a reverse direction with respect to a deviated angle direction of the polarization plane of the polarizer deviated by 45 degrees from the position of the analyzer. In this case, the polarization plane of the return light at the position of the polarizer is deviated by 45 degrees - (-45 degrees) = 90 degrees with respect to the polarization plane of the polarizer, and the polarization of the backward traveling light cannot be transmitted through the polarizer. In this way, the optical isolator functions to transmit and exit the forward traveling light and block the backward traveling return light.

[0004] As a material used as a Faraday rotator constituting the optical isolator, a TGG crystal (Tb3Ga5O12) and a TSAG crystal ((Tb 12 ) and a TSAG crystal ((Tb (3-x) Sc x )Sc2Al3O 12) are known in the related art (JP 2011-213552 A (Patent Literature 1) and JP 2002-293693 A (Patent Literature 2)). TGG crystals are currently widely installed as standard fiber laser devices. In addition, the Verdet constant of TSAG crystals is considered to be about 1.3 times the Verdet constant of TGG crystals, and this is also a material that can be installed on fiber laser devices, but since Sc is a very expensive raw material, there has been no progress in adoption due to production costs.

[0005] In addition to the above description, TAG crystals (Tb3Al5O 12 ) have also been known in the past as Faraday rotators, whose Verdet constant is greater than that of TSAG. However, since TAG crystals are decomposition-melting type crystals, there is a limitation that a perovskite phase is first generated at a solid-liquid interface and then a TAG phase is generated. That is, TAG crystals cannot grow in a state in which a garnet phase and a perovskite phase are constantly mixed, and the growth of large high-quality TAG crystals has not yet been achieved.

[0006] However, in recent years, WO 2018 / 193848 A (Patent Literature 3) discloses a paramagnetic garnet-type transparent ceramic that is a sintered body of a composite oxide represented by the following formula, and in which the linear transmittance at a wavelength of 1064 nm is 83% or more at a light path length of 15 mm (Tb 1-x-y Sc x Ce y )3(Al 1-z Sc z )5O 12 (in the formula, 0 < x < 0.08, 0 ≤y ≤ 0.01 and 0.004 < z < 0.16).

[0007] In addition, it has been disclosed that a dense ceramic sintered body having a composition of (Tb x Y 1-x )3Al5O 12 (x = 0.5 to 1.0) has a higher extinction ratio than existing TGG crystals (currently improved from 35 dB to 39.5 dB or more), and can also reduce the insertion loss (currently improved from 0.05 dB to 0.01 to 0.05 dB) (Non-Patent Literature 1).

[0008] Thereafter, JP 2019-199386 A (Patent Literature 4) discloses a paramagnetic garnet-type transparent ceramic which is a sintered body of a composite oxide represented by the following formula, includes SiO2 of more than 0 mass% and not more than 0.1 mass% as a sintering aid, and has a linear transmittance of 83.5% or more at a wavelength of 1064 nm under an optical path length of 25 mm (Tb 1-x- y Y x Sc y )3(Al 1-z Sc z )5O 12 wherein 0.05 ≤ x < 0.45, 0 < y < 0.1, 0.5 < 1-x-y < 0.95, and 0.004 < z < 0.2.

[0009] List of References

[0010] Patent Literature

[0011] Patent Literature 1: JP 2011-213552 A

[0012] Patent Literature 2: JP 2002-293693 A

[0013] Patent Literature 3: WO 2018 / 193848 A

[0014] Patent Literature 4: JP 2019-199386 A

[0015] Non-Patent Literature

[0016] Non-Patent Literature 1: Yan Lin Aung, Akio Ikesue, “Development of optical grade (TbxY1-x)3Al5O12 ceramics as Faraday rotator material”, J. Am. Ceram. Soc., (2017), 100(9), 4081-4087 SUMMARY

[0017] Problems to be Solved by the Invention

[0018] In Patent Literature 3, since the linear transmittance is improved to secure 83% or more even at an optical path length of 15 mm while having a Verdet constant comparable to TAG, it can be said that the performance almost reaches a practical level. However, although not described in Patent Literature 3, the inventors of the present application found that, in a case where laser having a wavelength of 1064 nm is incident on a sample (where the example of Patent Literature 3 is reproduced with an output of 100 W of incident power after the beam diameter is adjusted to 1.6 mm), the maximum amount of change in the incident laser beam diameter due to the generation of a thermal lens is greater than 15%.

[0019] Further, the material disclosed in Non-Patent Literature 1 is a material in which some of the Tb ions are substituted with Y ions, and thus, compared to the material of Patent Literature 3, the loss can be further reduced, and a very high-quality garnet-type Faraday rotator can be obtained. Specifically, since laser having a wavelength of 1064 nm is actually incident on a sample (where the material described in Non-Patent Literature is reproduced with an output of 100 W of incident power after the beam diameter is adjusted to 1.6 mm), it was found that the maximum amount of change in the incident laser beam diameter due to the generation of a thermal lens is less than 10%.

[0020] However, the material described in Non-Patent Literature 1 has a significantly low production reproducibility, and the inventors of the present application found that, in a case where laser having a wavelength of 1064 nm is incident on a sample (where the example of Non-Patent Literature is reproduced with an output of 100 W of incident power after the beam diameter is adjusted to 1.6 mm), the probability that the maximum amount of change in the incident laser beam diameter due to the generation of a thermal lens is greater than 15% is significantly high.

[0021] Similar to Non-Patent Literature 1, the material disclosed in Patent Literature 4 is a material in which some of the Tb ions are substituted with Y ions, and thus, a high-quality garnet-type Faraday rotator comparable to Non-Patent Literature 1 can be obtained. In a case where laser having a wavelength of 1064 nm is actually incident on a sample (where the material described in Patent Literature 4 is reproduced with an output of 100 W of incident power after the laser is adjusted to have a beam diameter of 1.6 mm), the maximum amount of change in the incident laser beam diameter due to the generation of a thermal lens is less than 10%, which is the same as in Non-Patent Literature 1. Further, the material described in Patent Literature 4 also significantly improves the production reproducibility.

[0022] Further, in a case where the incident power is further increased and laser light is incident on the sample in which the material described in Patent Document 4 is reproduced at an incident power output of 160 W, in most cases, the maximum amount of change in the incident laser beam diameter due to the generation of a thermal lens is greater than 15%. That is, it can be said that the composite oxide sintered body material for 100 W incident power has reached a practical level, but it still cannot be said that the composite oxide sintered body material for 160 W incident power has reached a practical level.

[0023] The present application has been made in view of the above-described circumstances, and an object of the present application is to provide: a terbium-containing paramagnetic garnet-type transparent ceramic in which, in a sintered body of a paramagnetic garnet-type oxide containing at least yttrium, terbium, and aluminum as main components and having a content volume molar concentration of terbium greater than or equal to that of yttrium, even in a case where the incident power of laser light having a wavelength of 1064 nm and a beam diameter of 1.6 mm is increased to 160 W, the maximum amount of change in the incident laser beam diameter can be kept below 10%; a manufacturing method thereof; a raw material mixture thereof; and a magneto-optical device obtained using the same and a production method thereof.

[0024] Means for solving the problem

[0025] To achieve the above object, according to a first aspect of the present application, there is provided a terbium-containing paramagnetic garnet-type transparent ceramic including a sintered body of a composite oxide represented by formula (1) containing terbium, yttrium, scandium, and aluminum: (Tb 1-x-y Y x Sc y )3(Al 1-z Sc z )5O 12 (1) (0.35 ≤ x ≤ 0.45, 0 < y < 0.03, 0.5 < 1-x-y < 0.65, 0.001 < z < 0.03, and 0 < y + z < 0.06), wherein the total light transmittance at a wavelength of 600 nm is 84.8% or more.

[0026] The terbium-containing paramagnetic garnet-type transparent ceramic of the present application can further include SiO2 in an amount greater than 0 mass% and not more than 0.1 mass% as a sintering aid.

[0027] In the terbium-containing paramagnetic garnet-type transparent ceramic of the present application, two optical end faces can be subjected to a precision mirror polishing process in a manner that the terbium-containing paramagnetic garnet-type transparent ceramic has a length of 14 mm or more, and each of the two polished optical end faces has an average roughness in a range of arithmetic mean height Sa ≤ 0.70 nm or root mean square height Sq ≤ 0.89 nm.

[0028] Preferably, the paramagnetic garnet-type transparent ceramic of the present application has a total light transmittance of 84.6% or more at a wavelength of 540 nm, and a total light transmittance of 85.25% or more at a wavelength of 1064 nm.

[0029] According to a second aspect of the present application, there is provided a magneto-optical material, the magneto-optical material comprising: a terbium-containing paramagnetic garnet-type transparent ceramic.

[0030] According to a third aspect of the present application, there is provided a magneto-optical device, the magneto-optical device comprising: the above magneto-optical material.

[0031] The magneto-optical device of the present application can be an optical isolator, the optical isolator comprising a terbium-containing paramagnetic garnet-type transparent ceramic as a Faraday rotator, comprising a polarizing material on the front side and the rear side of the optical axis of the Faraday rotator, and being usable in a wavelength band of 0.9-1.1 μm.

[0032] According to a fourth aspect of the present application, there is provided a production method for a terbium-containing paramagnetic garnet-type transparent ceramic, the terbium-containing paramagnetic garnet-type transparent ceramic comprising a sintered body of a composite oxide represented by formula (1), the composite oxide comprising terbium, yttrium, scandium, and aluminum: (Tb 1-x-y Y x Sc y )3(Al 1-z Sc z )5O 12 (1) (0.35 ≤ x ≤ 0.45, 0 < y < 0.03, 0.5 < 1-x-y < 0.65, 0.001 < z < 0.03, and 0 < y + z < 0.06), the production method including the steps of: mixing terbium oxide and yttrium oxide, or a co-precipitation oxide of terbium and yttrium, with aluminum oxide and scandium oxide to prepare a raw material mixture; subjecting the raw material mixture to a calcination treatment or a heating and drying treatment under a thermal history of 950°C or lower, and shaping the mixture to obtain a shaped body; debinding the shaped body to obtain a debound body; during sintering of the debound body under reduced pressure, first holding the debound body at a holding temperature of 1000°C or lower, degassing the debound body while holding the debound body in a state exhibiting a brown color originating from tetravalent terbium, and sintering the debound body by raising the temperature to a sintering temperature to obtain a sintered body having a relative sintered density in a range of 93.8% or higher and 97.2% or lower; subjecting the sintered body to a hot isostatic pressing (HIP) treatment to further densify the sintered body up to a relative sintered density of 99.9% or higher; subjecting the densified sintered body to a decoloration annealing treatment at a temperature lower than the temperature in the HIP treatment to decolor the brown color originating from tetravalent terbium exhibited by the densified sintered body; additionally sintering the decolored sintered body at a temperature higher than either of the sintering temperature and the temperature in the HIP treatment under reduced pressure; and subjecting the additionally sintered sintered body to an oxidation annealing treatment in an oxygen atmosphere or an air atmosphere at a temperature lower than the temperature in the HIP treatment.

[0033] In the raw material mixture, the proportion of the weight of the residue that does not pass through the screen having openings of 20 μm to the total weight of the raw material mixture is preferably 0.5% or lower.

[0034] According to a fifth aspect of the present application, there is provided a raw material mixture for producing a terbium-containing paramagnetic garnet-type transparent ceramic including a sintered body of a composite oxide represented by formula (1) containing terbium, yttrium, scandium, and aluminum: (Tb 1-x-y Y x Sc y )3(Al 1-z Sc z )5O 12 (1) (0.35 ≤ x ≤ 0.45, 0 < y < 0.03, 0.5 < 1-x-y < 0.65, 0.001 < z < 0.03, and 0 < y + z < 0.06), wherein the raw material mixture is mixed in a state where each oxide of terbium, yttrium, scandium, and aluminum is not combined, and the proportion of the weight of the residual portion of the screen mesh having an opening of 20 μm to the total weight of the raw material mixture is 0.5% or less.

[0035] According to a sixth aspect of the present application, there is provided a production method for a magneto-optical device, wherein the magneto-optical device comprises a paramagnetic garnet-type transparent ceramic obtained by a production method for a paramagnetic garnet-type transparent ceramic.

[0036] Effects of the Invention

[0037] According to the present application, it is possible to provide a terbium-containing paramagnetic garnet-type transparent ceramic which is truly transparent and can be sufficiently used for high-power laser applications, wherein even in the case of incidence of a high-power laser (for example, a laser having a wavelength of 1064 nm, a beam diameter of 1.6 mm, and an incident power of 160 W), the maximum variation amount of the incident laser beam diameter can be kept to 10% or less, and the shape of the incident beam does not collapse. Furthermore, by using the terbium-containing paramagnetic garnet-type transparent ceramic, it is possible to provide a magneto-optical device, such as a magneto-optical material and an optical isolator, which can be applied to a high-output laser device, and a production method for a magneto-optical device. BRIEF DESCRIPTION OF DRAWINGS

[0038] [ Figure 1 ] This is a schematic cross-sectional view showing a configuration example of an optical isolator in which the magneto-optical material according to the present application is used as a Faraday rotator.

[0039] [ Figure 2A ] This is a photograph showing the amount of gravel generated in the case where the raw material mixture of the terbium-containing garnet-type transparent ceramic according to the present application is subjected to calcination treatment at 900°C.

[0040] [ Figure 2B ] This is a photograph showing the amount of gravel generated in the case where the raw material mixture of the terbium-containing garnet-type transparent ceramic according to the present application is subjected to calcination treatment at 950°C.

[0041] [ Figure 2C ] This is a photograph showing the amount of gravel generated in the case where the raw material mixture of the terbium-containing garnet-type transparent ceramic according to the present application is subjected to calcination treatment at 1000°C.

[0042] [ Figure 3A ] This is a photograph showing the appearance of the sintered body after the HIP treatment of Example 3.

[0043] [ Figure 3B ] This is a photograph showing the appearance of the sintered body after the decoloring annealing treatment of Example 3.

[0044] Figure 3C This is a photograph showing the appearance of the sintered body of Comparative Example 6 after HIP processing.

[0045] Figure 4 This is a graph showing the total light transmittance of each sintered body after oxidation annealing processing in Example 3, Comparative Example 6, and Comparative Example 7. DETAILED DESCRIPTION

[0046] [1. Terbium-containing paramagnetic garnet-type transparent ceramic]

[0047] First, an embodiment of a terbium-containing paramagnetic garnet-type transparent ceramic according to the present application will be described. The terbium-containing paramagnetic garnet-type transparent ceramic according to the present embodiment includes a sintered body of a composite oxide represented by formula (1) containing terbium, yttrium, scandium, and aluminum: (Tb 1-x-y Y x Sc y )3(Al 1-z Sc z )5O 12 (1) (0.35 ≤ x ≤ 0.45, 0 < y < 0.03, 0.5 < 1-x-y < 0.65, 0.001 < z < 0.03, and 0 < y + z < 0.06), wherein the total light transmittance at a wavelength of 600 nm is 84.8% or more.

[0048] Since the sintered body has the composition of the composite oxide represented by formula (1), the light beam does not collapse even in the case of laser incidence having a wavelength of 1064 nm, a light beam diameter of 1.6 mm, and an incident power of 160 W.

[0049] It is preferable that the terbium-containing paramagnetic garnet-type transparent ceramic further contain SiO2 in an amount of more than 0 mass% and not more than 0.1 mass% as a sintering aid. From the viewpoint of improving the transparency of the sintered body of the paramagnetic garnet-type ceramic obtained to a level that is practical and stable, it is preferable that the amount of SiO2 be within the above range.

[0050] ​​In the present embodiment, it is necessary that the main components of the 6-coordination sites and the 4-coordination sites in the garnet structure are aluminum (Al). In a case where the main components at these sites can be formed of aluminum, the binding properties of the crystal are improved, and thus, the average value of dn / dt at a wavelength of 1064 nm at 30°C ± 10°C can be reduced. In a case where the ratio of the 6-coordination sites and the 4-coordination sites of aluminum is 1 - z (0.001 < z < 0.03), the average value of dn / dt at a wavelength of 1064 nm at 30°C ± 10°C can be controlled to 9.0 x 10 -6 K -1 The following.

[0051] In the present embodiment, terbium (Tb) and yttrium (Y) are selected as the main components at the 8-coordination sites, and the concentration of terbium is set to 1 - x - y (0.5 < 1 - x - y < 0.65), and the concentration of yttrium is set to x (0.35 ≤ x ≤ 0.45). In a case where the concentration of terbium is within the above range, the Verdet constant at a wavelength of 1064 nm is ensured to be 30 rad / (T·m) or more. Further, in a case where the concentration of terbium and the concentration of yttrium are set within the above range, even in a case of laser irradiation having a wavelength of 1064 nm, a beam diameter of 1.6 mm, and an incident power of 160 W, the beam does not collapse. Further, in a case where each of the two main components simultaneously satisfies the above range, both of the two characteristics can be satisfied simultaneously.

[0052] In the present embodiment, scandium (Sc) is added within the above range in formula (1). In formula (1), y satisfies 0 < y < 0.03, preferably 0.001 < y < 0.008, and more preferably 0.002 < y < 0.004. In a case where y is within the above range, the perovskite-type heterogeneous phase can be reduced to a level at which the perovskite-type heterogeneous phase is not detected by X-ray diffraction (XRD) analysis. Further, excessive reduction of the thermal conductivity due to the homogeneity of the sintered body or grain boundary scattering can be prevented. Further, in formula (1), z satisfies 0.001 < z < 0.03 and more preferably 0.002 < z < 0.004. In a case where z is within the above range, the perovskite-type heterogeneous phase can be reduced to a level at which the perovskite-type heterogeneous phase is not detected by X-ray diffraction (XRD) analysis. Further, excessive reduction of the thermal conductivity due to the homogeneity of the sintered body or grain boundary scattering can be prevented. Scandium is added within a range where y is greater than 0 and less than 0.03 and z is greater than 0.001 and less than 0.03, and thus, a highly transparent sintered body can be stably produced.

[0053] The terbium-containing paramagnetic garnet-type transparent ceramic of the present embodiment contains the above-described component having a composition represented by formula (1) as a main component. Here, "contains ~ as a main component" means that the ceramic contains 90 mass% or more of the complex oxide represented by formula (1). The content of the complex oxide represented by formula (1) is preferably 99 mass% or more, more preferably 99.9 mass% or more, still more preferably 99.99 mass% or more, and particularly preferably 99.999 mass% or more.

[0054] The terbium-containing paramagnetic garnet-type transparent ceramic of the present embodiment is composed of the above-described main component and a sintering aid used as a subcomponent, but can also contain other elements. Examples of the other elements include rare earth elements such as lutetium (Lu) and cerium (Ce), and various impurity groups such as sodium (Na), calcium (Ca), magnesium (Mg), phosphorus (P), tungsten (W), and molybdenum (Mo). In the case where the total amount of Tb and Y is set to 100 parts by mass, the content of the 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 (essentially zero).

[0055] The terbium-containing paramagnetic garnet-type transparent ceramic of the present embodiment has a total light transmittance of 84.8% or more at a wavelength of 600 nm, which indicates that the oxygen deficiency of the sintered body is very small. It has been confirmed that in the case where oxygen deficiency exists in the sintered body, absorption due to oxygen deficiency occurs around a wavelength of 600 nm, and the total light transmittance is less than 84.8%. That is, in the case where the total light transmittance at a wavelength of 600 nm is 84.8% or more, this means that absorption due to oxygen deficiency is minimized, and therefore, this indicates that the sintered body is truly transparent and practical, in which the shape of the incident light beam does not collapse even in the case where a high-power laser is incident with a wavelength of 1064 nm, a beam diameter of 1.6 mm, and an incident power of 160 W.

[0056] In the terbium-containing paramagnetic garnet-type transparent ceramic of the present embodiment, the total light transmittance is 84.8% or more at a wavelength of 540 nm, and 85.3% or more at a wavelength of 1064 nm. This indicates that there are no microbubbles having a size of 1 μm or less, which slightly reduce the total light transmittance at a wavelength of 540 nm, and there are no various defects such as residual distortion that reduce the total light transmittance at a wavelength of 1064 nm, and therefore, the sintered body is truly transparent.

[0057] The terbium-containing paramagnetic garnet-type transparent ceramic of the present embodiment is processed to adjust the length to 14 mm or more, and used for a desired magneto-optical material. Incident light in a wavelength band of 0.9-1.1 μm can be rotated by 45 degrees from the viewpoint of a correct magnetic circuit design (even though this depends on the constitution and size of an externally attached magnet), and it is preferable that the length be set to 14 mm or more.

[0058] It is preferable that both of the optical end faces of the terbium-containing paramagnetic garnet-type transparent ceramic of the present embodiment be optically polished in a manner that the average roughness is in the range of an arithmetic average height Sa ≤ 0.70 nm or a root mean square height Sq ≤ 0.89 nm. From the viewpoint that the laser damage threshold is 10 J / cm 2 From the above viewpoint, it is preferable that the average roughness of both of the optical end faces be in the above range. From the viewpoint that unintended scattering loss on the optical surface can be simultaneously suppressed to a minimum level, it is preferable that the average roughness thereof be in the above range.

[0059] [2. Production method of terbium-containing paramagnetic garnet-type transparent ceramic]

[0060] Next, an embodiment of a production method of a terbium-containing paramagnetic garnet-type transparent ceramic according to the present application will be described. The production method of the present embodiment includes the following steps: mixing oxides of terbium, yttrium, aluminum, and scandium to prepare a raw material mixture; performing a calcination process or a heating and drying process on the raw material mixture under a predetermined thermal history, and shaping the mixture to obtain a shaped body; debinding the shaped body to obtain a debound body; during sintering of the debound body under reduced pressure, first holding the debound body at a predetermined temperature, degassing the debound body while the debound body exhibits a state of brown color derived from tetravalent terbium, and sintering the debound body by raising the temperature to a sintering temperature to obtain a sintered body having a predetermined relative sintered density; performing a hot isostatic pressing (HIP) process on the sintered body to further densify the sintered body; performing a decoloration annealing process on the densified sintered body to decolor the brown color derived from tetravalent terbium; additionally sintering the decolored sintered body; and performing an oxidation annealing process on the additionally sintered sintered body. Hereinafter, each step will be described.

[0061] [2-1. Preparation step of raw material mixture]

[0062] As the raw material used in the production method of the present embodiment, for example, an oxide powder of each of terbium, yttrium, scandium, and aluminum can be used. The purity of the raw material here is preferably 99.9 mass% or more, and particularly preferably 99.99 mass% or more. Further, as the terbium and the yttrium, a co-precipitated oxide thereof can also be used. Further, a predetermined amount of each of the raw materials is weighed and mixed to have the composition of the composite oxide represented by formula (1), thereby obtaining a raw material mixture. Further, in the present specification, the "raw material mixture" indicates a mixture of the oxides of terbium, yttrium, scandium, and aluminum in an uncombined state.

[0063] As the sintering aid, silicon oxide (Si02) of more than 0 mass% and not more than 0.1 mass% can be added to the raw material mixture. As appropriate, the raw material mixture is subjected to a mixing treatment using a wet-type ball mill, a bead mill, or a jet mill.

[0064] Further, in the above raw material, it is preferable to subject the terbium oxide and the yttrium oxide or the co-precipitated oxide of terbium and yttrium to a preliminary baking treatment at a temperature of 1000°C or higher. From the viewpoint that the BET value of each of the raw materials is suppressed to 35 m 2 / g or less and that the dispersion of the ultrafine powder during the treatment can be prevented, it is preferable to subject the preliminary baking treatment at a temperature of 1000°C or higher, as described above. Further, since the moisture adsorbed in the raw material powder can be removed, the accuracy is improved by weighing the raw material subjected to the baking treatment.

[0065] It is preferable to subject the raw material mixture (in the case where the oxides of terbium and yttrium are subjected to a preliminary baking treatment, the raw material mixture obtained by mixing the oxides of terbium and yttrium with the aluminum oxide and the scandium oxide) to a calcination treatment or a heating and drying treatment. In the raw material mixture subjected to the calcination treatment or the heating and drying treatment, the thermal history is suppressed to preferably 950°C or lower, more preferably 920°C or lower, and still more preferably 900°C or lower. From the viewpoint that the possibility that the rare earth oxide component and the aluminum oxide can react and bond with each other to thereby transform into a monoclinic phase and / or a perovskite phase and / or a garnet phase can be suppressed, and that the formation of particles of the high-activity aluminum oxide fine powder while undergoing a necking reaction and aggregation can be suppressed, the thermal history of the raw material mixture is preferably controlled within the above range.

[0066] In the case where the thermal history of the raw material mixture is actually controlled within the above range, in the gravel, lumps, aggregates, and coarse powder (hereinafter also simply referred to as "gravel") derived from the reaction compounds and the necking aggregates, the amount of the residual portion that does not pass through the screen having openings of 20 μm can be suppressed to 0.5% or less in terms of the proportion of the weight of the residual portion to the total weight of the raw material mixture. Further, the lower limit of the thermal history in the calcination treatment or the heating and drying treatment of the raw material mixture is not particularly limited, but can be, for example, 800°C or higher.

[0067] Further, in the case where the raw material mixture is controlled as described above, since the abundance of the quasi-agglomerate component which hardly passes through the screen having 20 μm openings is also small, and the entire raw material mixture can be maintained in a fine powder state, the granules granulated by spray drying or the like have the characteristics of being soft, easily crushable, smooth, and having high flowability, and thus, the filling property and the crush resistance during the forming step can be maintained in a satisfactory state. In the case where the filling property and the crush resistance during the forming step are satisfactory, it is impossible to generate an undesirable void within the formed body, and it is possible to increase the overall forming density. Further, in the case where such a formed body is added in the sintering step, it is possible to obtain a highly transparent sintered body in which the number of residual bubbles is extremely small.

[0068] Further, in the case where the raw material mixture is controlled in the above-described state, since the reactivity of the raw material mixture is also maintained at a high level, it is possible to promote densification in the sintering step, and it is possible to perform uniform sintering until the inside of the sintered body. In this way, it is possible to obtain a sintered body which is highly transparent, has low compositional heterogeneity, is of high quality, and is free of a foreign phase.

[0069] For the purpose of improving the quality stability and the yield in the subsequent steps, various organic additives can be added to the raw material mixture. In the present embodiment, the organic additives are not particularly limited, and various dispersants, binders, lubricants, plasticizers, and the like can be appropriately used. However, it is preferable to select the types of these organic additives which do not contain unnecessary metal ions and have high purity. Further, the order of addition of each organic additive needs to be appropriately designed so that the control of the properties (particle size distribution, etc.) of the raw material mixture to be produced is not hindered.

[0070] [2-2. Forming step]

[0071] In the production method of the present embodiment, a typical pressing forming step can be appropriately used. That is, a most common uniaxial pressing step, which fills a mold and presses the mold in a specific direction, and a cold isostatic pressing (CIP) step or a warm isostatic pressing (WIP) step, which seals and houses a deformable waterproof container and presses the waterproof container with hydrostatic pressure, can be appropriately used. Furthermore, the applied pressure can be appropriately adjusted while confirming the relative density of the formed body to be obtained, and there is no particular limitation. For example, it is preferable that the applied pressure be controlled to be about 300 MPa or less from the viewpoint of reducing production costs, which can be operated by a commercially available CIP device or WIP device. Alternatively, a hot pressing step, a spark plasma sintering step, a microwave heating step, or the like, in which a forming step and sintering are simultaneously performed during forming, can be appropriately used. Furthermore, the formed body can be prepared by a casting forming method instead of a pressing forming method. A forming method such as pressure casting, centrifugal casting, and extrusion forming can also be employed by optimizing the combination of the shape and size of the oxide powder and various organic additives as raw materials. Furthermore, in order to prepare the high-quality terbium-containing paramagnetic garnet-type transparent ceramic of the present application, it is preferable that the applied pressure of the uniaxial pressing forming be as low as possible within a range in which the formed body does not collapse.

[0072] [2-3. Debinding Step]

[0073] In the production method of the present embodiment, a typical debinding step can be appropriately used. That is, heating and debinding can be performed by a heating furnace. Furthermore, the kind of the gas atmosphere here is not particularly limited, and air, oxygen, hydrogen, or the like can be appropriately used. It is preferable that the debinding temperature be higher than or equal to a temperature at which the organic components of the added organic additives can be sufficiently decomposed and removed, and the temperature range be controlled to be 900°C or lower. From the viewpoint of preventing an undesirable thermal shrinkage due to heating of the debound body in an atmosphere that is not a reduced pressure environment, in which densification is performed while adsorbed gas is incorporated, it is preferable that the temperature of the debinding treatment be controlled within the above range. It is more preferable that the debinding temperature be controlled to be 800°C or lower. Furthermore, the lower limit of the debinding temperature is not particularly limited, but can be, for example, 300°C or higher.

[0074] [2-4. Sintering Step]

[0075] In the production method of the present embodiment, the sintering step is a step in which, in the case where the debound body obtained in the debinding step is sintered under reduced pressure, the temperature is temporarily held in a temperature range of 1000°C or lower in the temperature rising, the debound body is degassed in a state in which the brown color derived from the tetravalent terbium oxide is maintained, and the temperature is increased to a sintering temperature to obtain a sintered body having a relative sintered density of 93.8% or more and 97.2% or less.

[0076] The reason for temporarily maintaining the temperature in the temperature range below 1000°C is to completely discharge the adsorbed components such as water vapor and nitrogen gas to the outside of the system before the densification is completely performed. However, it has been found that, although most of the oxygen component that is desorbed in the case where the tetravalent Tb in the terbium oxide component is changed to trivalent Tb by heating can be effectively discharged to the outside of the system by maintaining the temperature as described above (hereinafter also referred to as "holding"), oxygen combined with yttria is also desorbed at the same time and oxygen deficiency gradually occurs. In addition, it has also been found that, in the case where the tetravalent Tb is completely changed to trivalent Tb, the degree of oxygen deficiency of the yttria also becomes severe with the change and the amount of oxygen deficiency of the entire sintered body increases to the extent that the appearance becomes black after the subsequent HIP treatment.

[0077] Therefore, in the case where the desorption treatment of the adsorbed components is performed while the holding temperature for changing the tetravalent Tb to trivalent Tb is controlled to be below 1000°C, the tetravalent Tb remains in a small amount and the sintered body appears light brown, but the amount of oxygen deficiency in the yttria can be suppressed to a state that is extremely small. Therefore, the sintered body that can be obtained has an appearance that appears light brown (close to orange) without black after the subsequent HIP treatment, that is, has an extremely low oxygen deficiency.

[0078] In addition, in the case where the holding temperature is set to a temperature higher than 1000°C, a large amount of oxygen deficiency occurs to the extent that the appearance of the sintered body becomes black after the subsequent HIP treatment, instead of completely eliminating the light brown color. The lower limit of the holding temperature is not particularly limited, as long as the tetravalent Tb can be changed to trivalent Tb at the temperature, but for example, it is preferably 850°C or higher, more preferably 900°C or higher. In addition, the holding time during which the temperature is temporarily maintained at the holding temperature and degassing is performed can be several hours, which is sufficient, but in order to sufficiently perform degassing from the inside of the debindered body, it is preferable to set the holding time to 8 hours or more. The upper limit of the holding time is not particularly limited, but can be, for example, 30 hours or less.

[0079] In the sintering step, the temperature is temporarily maintained at the holding temperature and degassing is performed as described above, and the temperature is increased to a predetermined sintering temperature. The predetermined sintering temperature must be set in a temperature range in which only the garnet phase is stably obtained by combining the oxides of terbium, yttrium, and scandium with alumina. From the viewpoint that the generation rate of an undesirable heterogeneous phase such as a monoclinic phase and a perovskite phase can be suppressed to a minimum, it is preferable to heat the transparent ceramic sintered body to a temperature range in which only the garnet phase is generated as quickly as possible after the degassing process is sufficiently completed.

[0080] For example, the predetermined sintering temperature is preferably 1400°C to 1780°C, and particularly preferably 1450°C to 1700°C. As described above, from the viewpoint of promoting densification while suppressing heterogeneous precipitation, the sintering temperature is preferably in the above range. In addition, the temperature increase rate from the holding temperature to the sintering temperature is preferably 100°C / hr or more, more preferably 200°C / hr or more, and still more preferably 250°C / hr or more, which is a high rate of temperature increase. The upper limit of the temperature increase rate is not particularly limited, but can be, for example, 300°C / hr or less.

[0081] In the sintering step, the relative sintered density of the obtained sintered body is controlled to be in the range of 93.8% or more and 97.2% or less. The control of the relative sintered density can be performed by repeating preliminary experiments a plurality of times. It is more preferable to perform sintering while controlling the relative sintered density to be in the range of 93.8% or more and 96.5% or less, and still more preferable to perform sintering while controlling the relative sintered density to be in the range of 93.8% or more and 96.0% or less. In the case where the relative sintered density of the obtained sintered body is controlled to be in the above density range, residual air bubbles in the inside of the sintered body can be formed as closed pores. In addition, the sintered particle diameter can be controlled without excessively increasing, and thus, the closed pores can be sufficiently compacted in the subsequent HIP treatment, which is preferable.

[0082] In the sintering step, for example, a commonly used heating sintering such as an electric resistance heating method or an induction heating method can be appropriately used. The atmosphere here is set to a reduced pressure atmosphere (vacuum). In the case where the sintering treatment is performed in a reduced pressure atmosphere, components such as water vapor and nitrogen gas adsorbed in the inside of the debindered body can be efficiently volatilized and discharged, and oxygen gas that is largely desorbed in the case where tetravalent Tb is converted into trivalent Tb by heating can also be efficiently discharged and volatilized to the outside of the sintered body. The degree of vacuum is preferably 1 x 10 -3 From the viewpoint that the gas desorbed from the debindered body can be sufficiently discharged to the outside of the system and a homogeneous state can be reached until the center portion of the sintered body, the degree of vacuum is preferably controlled to be in the above range.

[0083] [2-5. Hot isostatic pressing (HIP) treatment step]

[0084] In the production method of the present embodiment, the hot isostatic pressing (HIP) treatment is performed after the sintering step, and the sintered body is densified until the relative sintered density of the sintered body reaches 99.9% or more. In the case where the relative sintered density in the sintering step is appropriately controlled, that is, in the case where the HIP treatment is performed in a state where the sintered particle diameter is not too large, the HIP stress is transmitted from the outer peripheral portion of the sintered body to the central portion of the sintered body widely and uniformly, the closed pores are compacted, and the sintered body is sufficiently densified. In other words, a substantially ideal sintered body, which has no stress unevenness, no undesirable void unevenness, and a small amount of remaining bubbles, can be obtained.

[0085] In the production method of the present embodiment, the conditions are controlled in such a manner that the sintered body intentionally exhibits a light brown appearance originating from tetravalent Tb remaining after the HIP treatment. In this manner, the occurrence of oxygen deficiency of yttria, which is easily reduced, can be suppressed, and thus a terbium-containing paramagnetic garnet-type transparent ceramic sintered body having a total light transmittance of 84.8% or more at a wavelength of 600 nm can be obtained. Further, in the case where yttria has oxygen deficiency, it has been confirmed that absorption caused by oxygen deficiency occurs in the vicinity of a wavelength of 600 nm, and the total light transmittance is less than 84.8%. In other words, the case where the total light transmittance at a wavelength of 600 nm is 84.8% or more indicates that absorption caused by oxygen deficiency is minimized, and thus a truly transparent and practical sintered body can be obtained, in which the shape of the incident light beam does not collapse even in the case of a high-power laser having an incident wavelength of 1064 nm, a light beam diameter of 1.6 mm, and an incident power of 160 W.

[0086] As the kind of the pressing gas medium used in the HIP treatment, an inert gas such as argon or nitrogen, or Ar-02 can be appropriately used. The pressure applied by the pressing gas medium is preferably 50 to 300 MPa, and more preferably 100 to 300 MPa. In the case where the pressure is less than 50 MPa, the effect of improving the transparency cannot be obtained in some cases. Further, in the case where the pressure is more than 300 MPa, further improvement of the transparency cannot be obtained even in the case where the pressure is increased and the load on the device is excessive, which can damage the device. It is preferable that the applied pressure be 196 MPa or less, which is a value that can be treated by a conveniently commercially available HIP device.

[0087] The processing temperature of the HIP processing is preferably 1100°C to 1780°C, more preferably 1200°C to 1730°C. A heat treatment temperature higher than 1780°C is not preferred because the risk of oxygen deficiency increases. Further, in the case where the heat treatment temperature is lower than 1100°C, the effect of improving the transparency of the sintered body is hardly obtained. Further, the holding time at the processing temperature is not particularly limited, but because of the risk of oxygen deficiency, it is not preferred to hold the processing temperature for an extremely long time. Generally, it is preferred to set the holding time to 1 to 3 hours.

[0088] The heater material, the heat insulating material, and the processing container for the HIP processing are not particularly limited. However, graphite, molybdenum (Mo), tungsten (W), and platinum (Pt) can be appropriately used, and yttria and gadolinia can also be appropriately used as the processing container. In particular, from the viewpoint that platinum can be used as the heater material, the heat insulating material, and the processing container, it is preferred that the processing temperature be 1500°C or lower, and Ar-O2 can be used as the pressurizing gas medium, which can prevent oxygen deficiency from occurring during the HIP processing. In the case where the processing temperature is higher than 1500°C, graphite is preferred as the heater material and the heat insulating material. In this case, it is preferred that any one of graphite, molybdenum, and tungsten be selected as the processing container, any one of yttria or gadolinia be selected as a double container within the processing container, and the container be filled with an oxygen releasing material from the viewpoint that the amount of oxygen deficiency occurring during the HIP processing can be suppressed as much as possible.

[0089] [2-6. Decolorization annealing processing step]

[0090] In the production method of the present embodiment, because the appearance of the sintered body that has been subjected to the HIP processing is in a state of appearing light brown, decolorization annealing processing is performed in an oxygen atmosphere or in an air atmosphere at a processing temperature lower than or equal to the processing temperature of the HIP processing, generally at 1200°C to 1400°C, for the purpose of decolorizing and substantially whitening the sintered body. This is because, in the case where this step is not performed and the subsequent additional sintering processing is performed, a large amount of bubbles remain in the sintered body. In the sintered body that has been subjected to the decolorization annealing processing, oxygen deficiency derived from yttria is suppressed to a minimum, and excess oxygen derived from tetravalent terbium is discharged to the outside of the system, and thus, a garnet-type oxide sintered body having extremely small defect absorption can be obtained.

[0091] The holding time at the temperature of the decolorization annealing processing does not necessarily need to be set long, and generally, it is sufficient to hold at the temperature for 2 hours.

[0092] [2-7. Additional sintering step]

[0093] In the production method of the present embodiment, after the decoloration annealing treatment, additional sintering is performed under reduced pressure at a temperature higher than the sintering temperature and also higher than the HIP treatment temperature. However, in the case where the temperature of the additional sintering is higher than 1780°C, the risk of oxygen deficiency increases, which is not preferred. In this way, residual internal deformation and bubbles can be further thoroughly eliminated. The degree of vacuum in the additional sintering step can be the same as that in the sintering step.

[0094] From the viewpoint that residual deformation and residual defects inside the sintered body can be recovered, the treatment time of the additional sintering is preferably set to 8 hours or more. The treatment time is more preferably 10 hours or more. In the case where the treatment time of the additional sintering is sufficiently long, residual deformation and residual bubbles can be sufficiently and uniformly removed from the outer peripheral portion to the central portion of the sintered body, which is preferred. In particular, in the case where the garnet-type transparent oxide ceramic material is used in an environment in which a high-power laser of 160 W or more is incident, the additional sintering step is an essential step.

[0095] [2-8. Oxidation annealing treatment step]

[0096] In the production method of the present embodiment, in order to recover oxygen deficiency in the obtained transparent ceramic sintered body, oxidation annealing treatment (oxygen deficiency recovery treatment) is preferably performed in an oxygen atmosphere or in the atmosphere after the completion of the additional sintering treatment, at a temperature below the HIP treatment temperature, typically 1000°C to 1500°C. Further, the oxidation annealing treatment temperature is more preferably 1300°C or higher and 1450°C or lower. In this way, even in the case of a sintered body in which oxygen deficiency has accumulated through sintering, HIP treatment, additional sintering, or the like, oxygen deficiency can be recovered, and a terbium-containing paramagnetic garnet-type transparent ceramic that is colorless and transparent and has no defect absorption can be obtained.

[0097] The treatment time of the oxidation annealing treatment is preferably 8 hours or more, more preferably 20 hours or more, and still more preferably 30 hours or more. In the case where the treatment time of the oxidation annealing treatment is sufficiently long, even oxygen deficiency remaining particularly in the central portion of the sintered body can be sufficiently recovered.

[0098] [2-9. Optical polishing step]

[0099] In the production method of the present embodiment, it is preferable to optically polish both end surfaces on the optical axis of the terbium-containing paramagnetic garnet-type transparent ceramic obtained by performing the above series of steps. In this case, the optical surface accuracy is preferably λ / 2 or less, and particularly preferably λ / 8 or less at a measurement wavelength λ of 633 nm. Furthermore, the average roughness of both optical end surfaces is preferably 0.70 nm or less in terms of the arithmetic average height Sa, and 0.89 nm or less in terms of the root mean square height Sq, particularly preferably Sa ≤ 0.55 nm and Sq ≤ 0.70 nm. Furthermore, as described above, by appropriately forming an anti-reflection film (AR coating film) on the optically polished surface, the light loss can be further reduced.

[0100] As described above, a terbium-containing paramagnetic garnet-type transparent ceramic including a composite oxide represented by Chemical Formula (1) and having a total light transmittance of 84.8% or more at a wavelength of 600 nm can be produced, the composite oxide including terbium, yttrium, scandium, and aluminum. Furthermore, by producing the terbium-containing paramagnetic garnet-type transparent ceramic under the above production conditions, a high value of the total light transmittance of 84.8% or more at a wavelength of 540 nm and 85.3% or more at a wavelength of 1064 nm can be obtained. This indicates that there are no microbubbles having a size of 1 μm or less that slightly reduce the total light transmittance at a wavelength of 540 nm, and there are no various defects such as residual distortion that reduce the total light transmittance at a wavelength of 1064 nm, and thus, a truly transparent sintered body is obtained. In the case where the total light transmittance is controlled within the above range, a truly transparent sintered body in which the shape of the incident light beam does not collapse even in the case where a high-power laser is incident with a wavelength of 1064 nm, a beam diameter of 1.6 mm, and an incident power of 160 W is provided.

[0101] [3. Magneto-optical material, magneto-optical device, and production method thereof]

[0102] Furthermore, an embodiment of the magneto-optical material, the magneto-optical device, and the production method thereof according to the present application will be described. The magneto-optical material of the present embodiment includes the above-described terbium-containing paramagnetic garnet-type transparent ceramic. Furthermore, the magneto-optical device of the present embodiment is configured by using the above-described terbium-containing paramagnetic garnet-type transparent ceramic. Specifically, it is preferable that the magneto-optical device is configured and used by applying a magnetic field parallel to the optical axis of the terbium-containing paramagnetic garnet-type transparent ceramic, and disposing a polarizer and an analyzer so that their optical axes are offset by 45 degrees from each other. In particular, the terbium-containing paramagnetic garnet-type transparent ceramic can be applied as a Faraday rotator to an optical isolator for a wavelength of 0.9 to 1.1 μm.

[0103] Figure 1This is a schematic cross-sectional view illustrating an example of an optical isolator as an optical element according to this embodiment, said optical isolator being a magneto-optical device comprising a Faraday rotator formed of paramagnetic garnet-type transparent ceramic. Figure 1 As shown, the optical isolator 100 includes a Faraday rotator 110 formed of the aforementioned paramagnetic garnet-type transparent ceramic within a housing 102, and a polarizer 120 and an analyzer 130 formed of polarizing materials. These are arranged along the optical axis 104 of the Faraday rotator in the order of polarizer 120, Faraday rotator 110, and analyzer 130. The polarization vibration surfaces of polarizer 120 and analyzer 130 are arranged at a relative angle of 45°. Furthermore, the optical isolator 100 includes a magnet 140 for applying a magnetic field to the Faraday rotator 110, specifically to at least one side surface of the Faraday rotator 110 within the housing 102.

[0104] This optical isolator 100 can be suitably used in industrial fiber laser devices (not shown). The optical isolator prevents reflected light from the laser emitted from the laser source from returning to the source, thus preventing oscillation instability.

[0105] Example

[0106] The present invention will be described in more detail below with reference to embodiments and comparative examples, but the present invention is not limited to the following embodiments.

[0107] [Examples 1 and 2, and Comparative Examples 1 to 8]

[0108] Terbium oxide powder, yttrium oxide powder, and scandium oxide powder manufactured by Shin-Etsu Chemical Industry Co., Ltd., and alumina powder manufactured by Taimei Chemical Co., Ltd. In addition, a liquid form of tetraethyl orthosilicate (TEOS) manufactured by Kishida Chemical Co., Ltd. was obtained. For all powder raw materials, the purity was 99.95% by mass or higher, and for the liquid raw materials, the purity was 99.999% by mass or higher.

[0109] Composite oxide raw materials having the two final compositions listed in Table 1 were prepared by adjusting the mixing ratio of the above-mentioned raw materials. As a method for adjusting the mixing ratio, each oxide powder was weighed and mixed such that the molar amounts of terbium, yttrium, aluminum, and scandium reached the molar ratios of the corresponding compositions in Table 1. Subsequently, TEOS was weighed and added to each raw material such that the amount added reached the values ​​listed in Table 1 as SiO2 (in mass %).

[0110] [Table 1]

[0111] Further, each of the components was dispersed and mixed in ethanol in an alumina ball mill device while taking care not to mix each of the components together. The treatment time was set to 15 hours.

[0112] Thereafter, each of the raw material mixtures was dried by performing a spray drying treatment, calcined while vibrating, the calcination temperature is listed in Table 2, and each of the samples was dispersed and mixed in ethanol in an alumina ball mill device while taking care not to mix each of the samples together. The treatment time was set to 20 hours. In this case, after 20 hours of mixing, the slurry of each of the raw materials was filtered through a screen having an opening of 20 μm, and the weight of the residual portion (grit) remaining on the screen was measured and recorded as a proportion of the total weight of the raw material mixture. The results are collectively listed in Table 2.

[0113] [Table 2]

[0114] Further, Figures 2A to 2C is a photograph showing the amount of grit of Sample 1, Sample 2, and Sample 3 remaining after the samples were mixed in ethanol and pulverized for 20 hours and passed through a screen having an opening of 20 μm after the calcination treatment.

[0115] As Figure 2C indicated, in the case where the raw material mixture was subjected to a calcination treatment at 1000°C, a large amount of coarse grit that could not pass through a screen having an opening of 20 μm was produced, and also a very large amount of coarse powder component that could barely pass through a screen having an opening of 20 μm was produced. Therefore, the obtained raw material was a raw material powder having a large size inhomogeneity, and was extremely hard, which was extremely difficult to handle. Naturally, even after the raw material mixture was granulated, the variation in hardness of the granules was worse, and the inhomogeneity of the pulverization performance was greater. Further, in the case where a shaped body was prepared using such a non-homogeneous raw material, it was not possible to prevent the occurrence of inhomogeneous stress transmission and the occurrence of unintended coarse voids within the shaped body. Then, in the case where the shaped body in such a non-homogeneous state was sintered, stress inhomogeneity, final composition inhomogeneity due to voids, and local internal defects were inevitably left within the sintered body. Further, in the case where the raw material mixture was subjected to a calcination treatment at 950°C, the amount of grit was significantly reduced as indicated in Figure 2B , and in the case where the raw material mixture was subjected to a calcination treatment at 900°C, almost no grit was found as indicated in Figure 2A .

[0116] Thereafter, the obtained six types of samples (oxide raw materials) were subjected to uniaxial press forming and CIP forming processes to obtain nine CIP formed bodies, respectively. All of the obtained formed bodies were subjected to a debinding process in a muffle furnace at 800°C for 3 hours to obtain debound formed bodies.

[0117] Subsequently, in the samples, sample 1 and sample 2 and sample 4 and sample 5 were each divided into three groups having three debound formed bodies. For the formed bodies of the classified samples 1 to 6, 6 samples in which the temperature during the temperature increase in the vacuum sintering step was set to 1000°C for 12 hours were prepared, and 3 samples in which the temperature was maintained at 1080°C for 12 hours were prepared. Further, for the 6 samples in which the temperature was maintained at 1000°C for 12 hours, the vacuum sintering process was performed by adjusting the sintering temperature to be different as listed in Table 3, thereby producing a difference in density after sintering. Further, for sample 3 and sample 6, the holding temperature during the temperature increase was fixed at 1000°C for 12 hours, and the sintering process was performed at a sintering temperature that made the relative sintering density in the range of 93.8% or more and 97.2% or less.

[0118] [Table 3]

[0119] Each of the obtained sintered bodies was charged into a HIP furnace made of a carbon heater, and the sintered body was subjected to a HIP process in Ar at 200 MPa and 1600°C for 3 hours. In all of the obtained sintered bodies, the relative density was 99.9% or more. Further, the appearance thereof exhibited a light brown color (color derived from tetravalent Tb) at a holding temperature of 1000°C, and exhibited a completely black color (a large amount of oxygen deficiency absorption) at a holding temperature of 1080°C.

[0120] Accordingly, all of the samples of Example 1 to Example 4 and Comparative Example 2, Comparative Example 4, Comparative Example 5, Comparative Example 7, Comparative Example 9, and Comparative Example 10, which exhibited a light brown appearance, were decolored by being subjected to a decoloring annealing process at 1300°C for 2 hours in an atmospheric heating furnace. The obtained annealed products were all in a transparent or translucent state, i.e., in a state in which the products were decolored.

[0121] Figure 3A is a photograph showing the appearance of the sintered body after the HIP process of Example 3, and the sintered body exhibited a light brown color. Figure 3B is a photograph showing the appearance of the sintered body after further subjecting to a decoloring annealing process at 1300°C for 2 hours in Example 3, and the sintered body was transparent. In contrast, Figure 3CThe photograph shows the appearance of the sintered body in Comparative Example 6, which has been held at a holding temperature of 1080°C for 12 hours, sintered by raising the temperature to the sintering temperature, and subjected to HIP treatment, and the sintered body is black.

[0122] Subsequently, for all samples including the blackened HIP-treated sintered bodies, an additional sintering was attempted in a vacuum sintering furnace at a sintering temperature of 1720°C for 15 hours to remove residual bubbles from the entire region, including the central part of the sintered body.

[0123] Subsequently, each of the obtained sintered bodies was subjected to oxidation annealing at 1400 °C for 40 hours in an atmospheric heating furnace, while controlling each batch (Example No. and Comparative Example No.) to fully recover deformation and oxygen loss. In this way, a total of 14 groups of sintered bodies of various types were prepared, including Examples and Comparative Examples, each group comprising at least 3 sintered bodies, and in some cases including 9 sintered bodies.

[0124] Subsequently, all obtained sintered body samples were cut and precision polished to a length of 20 mm. It was confirmed that the two optical end faces of all sintered body samples were treated under the conditions of optical surface accuracy λ / 8 (at a measurement wavelength of 633 nm) or higher, average roughness of less than 0.70 nm in terms of arithmetic mean height Sa, and root mean square height Sq of less than 0.89 nm.

[0125] For each of the sintered samples obtained as described above, the total transmittance and forward scattering rate were measured as follows.

[0126] (Methods for measuring total transmittance and forward scattering)

[0127] Total transmittance and forward scattering were measured according to JIS K 7105 (ISO 13468-2: 1999) and JIS K 7136 (ISO 14782: 1999). Measurements were performed at each wavelength of 540 nm, 600 nm, 760 nm, 930 nm, and 1064 nm using a spectrophotometer V-670 (manufactured by JASCO Corporation).

[0128] First, in the measurement of total transmittance, no workpiece (sample) is placed in the spectrophotometer V-670. Light, after being dispersed by the spectrometer, is emitted, received by an integrating sphere pre-positioned in the device, and the concentrated light is received by a detector. The obtained illuminance is denoted by I0. Subsequently, the workpiece is placed in the device, and the dispersed light is then incident on the workpiece. The transmitted light is again collected by the integrating sphere and received by the detector. The obtained illuminance is denoted by I and determined by the following equation.

[0129] Total transmittance (% / 25 mm) = I / I0 x 100

[0130] Then, in the measurement of the forward scattering, from the same system in the state in which the workpiece is set, the split light is again incident on the workpiece, and the transmitted light is again collected through the integrating sphere, and received by the detector, but the reflection plate on the rear surface of the integrating sphere is removed. The obtained illuminance represents the scattering component other than the linear transmission component, and is represented as I S and is obtained by the following equation. However, since the forward scattering is generally almost flat in the visible light range and does not have wavelength dependence, the value at the wavelength of 1064 nm is recorded as a representative value.

[0131] Forward scattering rate (% / 25 mm) = I S / I0 x 100

[0132] Further, in order to consider the influence of reproducibility or variation, 3 or 9 samples were measured under all conditions, and the average thereof was calculated to obtain the total transmittance and forward scattering value of each sample. Further, regardless of the diameter of the sintered body, a light beam having a diameter of 2 mm was used, and the incident position was adjusted to be substantially the center of the optically effective surface. Summarizing the above results, the total transmittance at wavelengths of 540 nm, 600 nm, 760 nm, 930 nm, and 1064 nm, and the forward scattering rate at a wavelength of 1064 nm are listed in Table 4. Further, Figure 4 A graph showing the total transmittance of Example 3, Comparative Example 6, and Comparative Example 7 is shown.

[0133] [Table 4]

[0134] As shown in the results listed in Table 4, in the preparation of the composite oxide sintered body of the present application, it was confirmed that, in the group in which the calcination temperature of the starting material mixture is controlled to be below 950°C, i.e., the group in which the uncombined raw material ratio is less than 1 / 2, the holding temperature during the temperature rise in the sintering step is set to 1000°C and the sample is sintered in a manner that the relative sintered density is less than 98.9% and preferably 97.2% or less and the HIP treatment is performed, i.e., all samples of Example 1 to Example 4, were processed into a truly transparent terbium-containing paramagnetic garnet-type transparent ceramic in which the total transmittance at a wavelength of 600 nm is 84.8% or more, the total transmittance at a wavelength of 540 nm is 84.6% or more, and the total transmittance at a wavelength of 1064 nm is 85.25% or more, and there is no significant absorption in a wide wavelength range.

[0135] On the other hand, in the samples of the group in which the calcination temperature of the raw material mixture was set to 1000°C (Comparative Example 5 and Comparative Example 10), the total light transmittance at a wavelength of 600 nm did not reach 84.8%, the total light transmittance at a wavelength of 540 nm did not reach 84.6%, and the total light transmittance at a wavelength of 1064 nm did not reach 85.25%.

[0136] Further, in the group in which the calcination temperature of the raw material mixture was controlled to be 950°C or lower, but the holding temperature during the temperature rise in the sintering step was set to 1080°C (Comparative Example 1, Comparative Example 3, Comparative Example 6, and Comparative Example 8) and the relative sintered density was greater than 97.2% (Comparative Example 2, Comparative Example 4, Comparative Example 7, and Comparative Example 9), the total light transmittance at a wavelength of 600 nm did not reach 84.8%, the total light transmittance at a wavelength of 540 nm did not reach 84.6%, and the total light transmittance at a wavelength of 1064 nm did not reach 85.25%.

[0137] Finally, in the samples in which the forward scattering was 0.5% or more (Comparative Example 2, Comparative Example 4, Comparative Example 5, Comparative Example 7, Comparative Example 9, and Comparative Example 10), the high-power resistance evaluation was abandoned because, in the case where a high-power laser beam having an incident power of 160 W was incident, the scattered light was scattered in four directions, and the evaluation became dangerous, and for the 8 groups of Example 1 to Example 4 and Comparative Example 1, Comparative Example 3, Comparative Example 6, and Comparative Example 8, the beam diameter change rate was evaluated in the case where a high-power laser beam having an incident power of 160 W was incident after the two optical end faces were coated with a reflection-reducing film at a wavelength of 1064 nm.

[0138] (Evaluation of the beam diameter change rate)

[0139] In the measurement of the beam diameter change rate, a collimated CW laser (manufactured by IPG Photonics Corporation) having a wavelength of 1070 nm, an exit power of 160 W, and a diameter of 1.6 mm was used, and a ModeMaster PCM 2A beam propagation analyzer (manufactured by Coherent Inc.) measured the beam diameter in the reference plane (entire surface frame) of the profiler. However, since the exit power after sample transmission was extremely high, the exit laser was first attenuated to 1 / 1000 or less of the intensity by a beam splitter, and then introduced into the beam profiler. The distance between the reference plane (entire surface frame) of the beam profiler and the sample holder was 1.9 m, and the distance between the reference plane and the collimator was 2.1 m. First, the beam diameter of the original beam was measured, and the value at this time was denoted by r0. Next, each sample of a length of 20 mm was placed in the optical path, the beam diameter of the transmitted light was measured and denoted by r. In the present invention, the beam diameter change rate was obtained by calculating |(1 - r / r0)| x 100, and was evaluated as acceptable in the case of 10% or less, and as unacceptable in the case of more than 10%. The evaluation results are listed in Table 5.

[0140] [Table 5]

[0141] As shown in the results listed in Table 5, in all groups in the embodiments in which the total light transmittance at a wavelength of 600 nm was 84.8% or more, the total light transmittance at a wavelength of 540 nm was 84.6% or more, and the total light transmittance at a wavelength of 1064 nm was 85.25% or more, the beam diameter change rate in the case of high-power laser beam incidence with an incident power of 160 W was 10% or less. In contrast, in all groups of Comparative Example 1, Comparative Example 3, Comparative Example 6, and Comparative Example 8 in which the values of the total light transmittance did not reach the above values, the beam diameter change rate in the case of high-power laser beam incidence with an incident power of 160 W was more than 10%, which indicated deterioration.

[0142] Further, although the present invention has been described based on the above-described embodiments, the present invention is not limited to the embodiments, and changes such as other embodiments, additions, changes, and deletions can be made within a range that a person skilled in the art can conceive, and as long as the actions and effects of the present invention are exhibited in all aspects, the changes also fall within the scope of the present invention.

[0143] List of Reference Symbols

[0144] 100 optical isolator

[0145] 102 housing

[0146] 110 Faraday rotator

[0147] 120 polarizer

[0148] 130 analyzer

[0149] 140 magnet

Claims

1. A terbium-containing paramagnetic garnet-type transparent ceramic comprising a sintered body of a complex oxide represented by formula (1) that contains terbium, yttrium, scandium, and aluminum: Terbium Yttrium Scandium Aluminum x y z (1) wherein 0.35 < x < 0.45, 0 < y < 0.03, 0.5 < 1-x-y < 0.65, 0.001 < z < 0.03, and 0 < y+z < 0.06, and wherein the total light transmittance at a wavelength of 600 nm is 84.8% or more. (Tb 1-x-y Y x Sc y )3(Al 1-z Sc z )5O 12 (1) 2. The terbium-containing paramagnetic garnet-type transparent ceramic according to claim 1, further comprising Si02 as a sintering aid in an amount of more than 0 mass% and not more than 0.1 mass%. two optical end faces of the terbium-containing paramagnetic garnet-type transparent ceramic are subjected to a precision mirror polishing process, and the average roughness of each of the two optical end faces subjected to the polishing process is in a range of an arithmetic average height Sa < 0.70 nm or a root mean square height Sq < 0.89 nm.

4. The terbium-containing paramagnetic garnet-type transparent ceramic according to claim 1 or 2, wherein the terbium-containing paramagnetic garnet-type transparent ceramic has a total light transmittance of 84.6% or more at a wavelength of 540 nm, and a total light transmittance of 85.25% or more at a wavelength of 1064 nm.

3. The terbium-containing paramagnetic garnet transparent ceramic according to claim 1 or 2, wherein 5. A magneto-optical material comprising the terbium-containing paramagnetic garnet-type transparent ceramic according to claim 1 or 2.

6. A magneto-optical device comprising the magneto-optical material according to claim 5.

7. The magneto-optical device according to claim 6, wherein the magneto-optical device is an optical isolator that comprises the terbium-containing paramagnetic garnet-type transparent ceramic as a Faraday rotator, comprises a polarizing material on the front side and the back side of the optical axis of the Faraday rotator, and is usable for a wavelength band of 0.9-1.1 μm.

8. A production method for a terbium-containing paramagnetic garnet-type transparent ceramic comprising a sintered body of a complex oxide represented by formula (1) that contains terbium, yttrium, scandium, and aluminum: Terbium Yttrium Scandium Aluminum x y z (1) wherein 0.35 < x < 0.45, 0 < y < 0.03, 0.5 < 1-x-y < 0.65, 0.001 < z < 0.03, and 0 < y+z < 0.06, the production method comprising the steps of: mixing a terbium oxide and a yttrium oxide, or a co-precipitation oxide of terbium and yttrium, with an aluminum oxide and a scandium oxide to prepare a raw material mixture; subjecting the raw material mixture to a calcination process or a heating and drying process under a thermal history of 950°C or less, and shaping the mixture to obtain a shaped body; debinding the shaped body to obtain a debound body; and sintering the debound body to obtain the terbium-containing paramagnetic garnet-type transparent ceramic.

9. The production method according to claim 8, wherein the raw material mixture is prepared by mixing the terbium oxide and the yttrium oxide, or the co-precipitation oxide of terbium and yttrium, with the aluminum oxide and the scandium oxide in a weight ratio of 0.5 < x < 0.65 : 0.001 < z < 0.03 : 0.35 < x+y+z < 0.

45. ​ (Tb 1-x-y Y x Sc y )3(Al 1-z Sc z )5O 12 (1) ​ ​ ​ ​ ​ during sintering of the debound body under reduced pressure, first holding the debound body at a holding temperature of 1000°C or lower, degassing the debound body while holding the debound body in a state exhibiting a brown color derived from tetravalent terbium, and sintering the debound body by raising the temperature to a sintering temperature, to obtain a sintered body having a relative sintered density in a range of 93.8% or greater and 97.2% or lower; subjecting the sintered body to a hot isostatic pressing (HIP) treatment to further densify the sintered body until the relative sintered density reaches 99.9% or greater; subjecting the densified sintered body to a decoloration annealing treatment at a temperature lower than that in the HIP treatment to decolor the brown color derived from the tetravalent terbium exhibited by the densified sintered body; further sintering the decolored sintered body at a temperature higher than either of the sintering temperature and the temperature in the HIP treatment under reduced pressure; and subjecting the further sintered sintered body to an oxidation annealing treatment at a temperature lower than that in the HIP treatment in an oxygen atmosphere or an air atmosphere.

9. The production method for a terbium-containing paramagnetic garnet-type transparent ceramic according to claim 8, wherein a proportion of a weight of a residual portion that does not pass through a screen having openings of 20 μm to a total weight of the raw material mixture is 0.5% or less in the raw material mixture.

10. A raw material mixture for producing a terbium-containing paramagnetic garnet-type transparent ceramic containing a sintered body of a composite oxide represented by formula (1) that contains terbium, yttrium, scandium, and aluminum: Tb1-x-y-zScxYyAlzO3 (1) wherein 0.35 ≤ x ≤ 0.45, 0 < y < 0.03, 0.5 < 1-x-y < 0.65, 0.001 < z < 0.03, and 0 < y + z < 0.06, wherein the raw material mixture is mixed in a state in which oxides of terbium, yttrium, scandium, and aluminum are not combined, and a proportion of a weight of a residual portion that does not pass through a screen having openings of 20 μm to a total weight of the raw material mixture is 0.5% or less. (Tb 1-x-y Y x Sc y )3(Al 1-z Sc z )5O 12 (1) 11. A method for producing a magneto-optical device, wherein the magneto-optical device contains the paramagnetic garnet-type transparent ceramic obtained by the production method for a paramagnetic garnet-type transparent ceramic according to claim 8 or 9. ​ ​ ​

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