Ceramic material, optical member, head-mounted display, and method for producing ceramic material

Abstract

In the present invention, visible light is appropriately refracted and transmitted. This ceramic material (10) contains, as a principal component, a compound having a perovskite structure represented by chemical formula AxBOz, wherein: A contains an alkaline earth metal element as a principal component; B contains Ti as a principal component; at least one of A and B contains a rare earth element; x is 0.9-1.0; z is a numerical value that satisfies the charge neutrality of the entire chemical formula; and the total light transmittance at a thickness of 1 mm with respect to light having a wavelength of 635 nm is 10% or greater.

Description

Ceramic material, optical member, head-mounted display, and method for manufacturing ceramic material

[0001] The present invention relates to a ceramic material, an optical member, a head-mounted display, and a method for manufacturing a ceramic material.

[0002] In recent years, there has been a demand for materials with high refractive indexes and high transmittances. In particular, as shown in Patent Document 1, for example, in wearable devices such as head-mounted displays that realize AR (Augmented Realitx), VR (Virtual Realitx), MR (Mixed Realitx), etc., light guide plates are required to have high refractive indexes and high transmittance for visible light. Furthermore, Patent Document 2 describes a translucent ceramic whose main component is a perovskite compound.

[0003] International Publication No. 2022 / 234782 Patent No. 4747892

[0004] However, there is room for improvement in terms of transmitting visible light while still appropriately refracting it.

[0005] An object of the present invention is to provide a ceramic material, an optical member, and a head-mounted display that can transmit visible light while appropriately refracting the same.

[0006] The ceramic material according to the present disclosure is A x BO ｚ wherein A is an alkaline earth metal element as a main component, B is Ti as a main component, at least one of A and B contains a rare earth element, x is 0.9 or more and 1.0 or less, z is a value that establishes charge neutrality in the entire chemical formula, and the total light transmittance at a thickness of 1 mm for light with a wavelength of 635 nm is 10% or more.

[0007] The optical member according to the present disclosure uses the ceramic material as a light guide plate.

[0008] The head mounted display according to the present disclosure uses the ceramic material as a light guide plate member.

[0009] The method for producing a ceramic material according to the present disclosure includes mixing solid raw materials, shaping the mixed raw materials to obtain a molded body, and sintering the molded body in an oxygen atmosphere to obtain the ceramic material.

[0010] According to the present invention, visible light can be transmitted while being appropriately refracted.

[0011] FIG. 1 is a schematic diagram of a ceramic material according to this embodiment.

[0012] Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that the present invention is not limited to these embodiments, and when there are multiple embodiments, the present invention also includes combinations of the embodiments. Numerical values ​​include rounding ranges. In addition, in this embodiment, lower and upper limits can be appropriately combined. For example, if a lower limit is listed for a certain parameter and an upper limit is listed for that parameter, the parameter may have any value selected from the listed lower limit values ​​as its lower limit and any value selected from the listed upper limit values ​​as its upper limit.

[0013] (Ceramic Material) FIG. 1 is a schematic diagram of a ceramic material according to this embodiment. The ceramic material 10 according to this embodiment is a translucent member capable of transmitting visible light. The ceramic material 10 is preferably a polycrystalline ceramic, and it can also be said that a polycrystalline ceramic sintered body is preferable. As shown in FIG. 1, the ceramic material 10 according to this embodiment is a plate-shaped member, but the shape of the ceramic material 10 is not limited to a plate shape and may be any shape. In this embodiment, the ceramic material 10 is used as an optical element. More specifically, in this embodiment, the ceramic material 10 is used as a light guide plate. That is, in this embodiment, an optical member using the ceramic material 10 as a light guide plate can be provided. Examples of the optical member here include display devices. More specifically, the ceramic material 10 is used as a light guide plate for a head-mounted display. A head-mounted display is a display device (wearable device) worn on a person's head. However, the ceramic material 10 can be used for any purpose, and is not limited to being used as a light guide plate or a head-mounted display. For example, the ceramic material 10 is also useful as a base substrate for growing other materials, a transparent substrate for a capacitance sensor for remote sensing, a low-voltage driven electrostatic induction panel substrate, jewelry and furnishings, cover glass and housings for mobile terminals and wearable devices, interiors and non-contact panel covers for automobiles and other mobile bodies, dielectric antennas, window materials for generating surface microwave plasma, and droplet control digital microchannel substrates.

[0014] (A x BO ｚ ) The ceramic material 10 is A x BO ｚThe ceramic material 10 contains, as a main component, a compound (oxide) with a perovskite structure represented by the chemical formula: In other words, the compound that is the main component can be said to be an oxide in which one or more types of element A are located at the A site in the perovskite structure, one or more types of element B are located at the B site in the perovskite structure, and O (oxygen element) is located at the O site in the perovskite structure. The main component here may refer to a content of the element relative to the entire ceramic material 10 that is more than 50% by mass. The ceramic material 10 contains the main component A. x BO ｚ The content of the main component is preferably 90% or more and 100% or less, and more preferably 95% or more and 100% or less, by mass ratio relative to the entire ceramic material 10. The content of the main component can be evaluated by quantitative analysis using powder X-rays. When two or more elements are contained as element A, one of these elements will be located at each A site of the perovskite structure, and the same applies to the following description of the B site.

[0015] A, the main component of the ceramic material 10 x BO ｚ contains a rare earth element in at least one of the A site and the B site. x BO ｚ The rare earth elements contained in the above are substitutional elements in the A site or B site, and it can be said that at least a portion of the main component elements in the A site or B site are substituted with the rare earth element. In this way, by including a rare earth element in at least one of the A site and the B site, the rare earth element enters at least one of the divalent and tetravalent sites, making it easier for defects to occur in the crystal, thereby improving sinterability. This makes it possible to transmit visible light while appropriately refracting it. Specific examples of the inclusion form of the rare earth element will be described later.

[0016] (Element A) (Main component) A x BO ｚIn the formula, A is an element located at the A site in the perovskite structure. In the first embodiment, element A is mainly composed of an alkaline earth metal element. That is, it can be said that the main component of the elements located at the A site (the element with the highest content among the elements located at the A site) is an alkaline earth metal element. The alkaline earth metal element as the main component contained in element A is preferably at least one of Ca, Sr, and Ba, more preferably at least one of Sr and Ba, and more preferably Sr. Furthermore, it is also preferable that the alkaline earth metal element as the main component contained in element A includes Sr and at least one of Ca and Ba.

[0017] Ceramic material 10A x BO ｚ In the formula, the ratio of the amount of alkaline earth metal element (alkaline earth metal element located at the A site) contained in element A to the total amount of each element A (each element located at the A site) (amount of alkaline earth metal element / total amount of element A) is 50% or more, preferably 70% or more and 99.9% or less, more preferably 90% or more and 99.5% or less, and even more preferably 97% or more and 99.4% or less, in molar ratio. When the amount of alkaline earth metal element contained in the A site is within this range, visible light can be appropriately refracted and transmitted. Note that, when element A contains multiple types of alkaline earth metal elements, the amount of alkaline earth metal element contained in element A here refers to the total amount of these alkaline earth metal elements.

[0018] Furthermore, when element A contains multiple alkaline earth metal elements, the ratio of the amount of Sr contained in element A to the total amount of alkaline earth metal elements contained in element A (amount of Sr / total amount of alkaline earth metal elements) is preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more, in molar ratio. When the amount of Sr contained in the A site is within this range, it becomes possible to transmit visible light while appropriately refracting it. Since the substitution of Ca or Ba lowers the melting point of the material, the calcination temperature and sintering temperature can be reduced, resulting in the effect of high quality due to low-temperature sintering. Furthermore, when element A contains multiple alkaline earth metal elements, element A preferably contains Sr and Ca. In this case, the ratio of the amount of Ca contained in element A to the total amount of alkaline earth metal elements contained in element A (amount of Ca / total amount of alkaline earth metal elements) is preferably 0% to 8% in molar ratio, more preferably 0% to 6%, even more preferably 2% to 6%, still more preferably 2% to 5%, and still more preferably 2% to 4%. In this case, the remainder of element A (elements other than Ca) is preferably Sr.

[0019] Whether or not a specific element is contained in a perovskite crystal can be analyzed by techniques such as peak shift of diffraction lines in X-ray diffraction (XRD), structural analysis such as the Rietveld method, or X-ray absorption fine structure (EXAFS) analysis. The content of the element can be measured by X-ray fluorescence analysis (XRF).

[0020] (Rare Earth Element) Element A preferably contains a rare earth element as a substitution component (subcomponent). The rare earth element contained in element A is preferably at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and is preferably at least one of La, Sm, Eu, Gd, Tb, Ho, Yb, and Lu, and more preferably at least one of Sm, Gd, Tb, Yb, and Lu. By including such a rare earth element in element A, it is possible to improve sinterability and transmit visible light while appropriately refracting it. In addition, by including a rare earth element in element A, vacancy defects occurring at the position in the crystal lattice of element A, or the position in the crystal lattice of element B, or at oxygen positions, or element defects accompanying light absorption occurring at the crystal particle interface, impurities such as adjusters, etc. are balanced in a charge-neutral relationship, which also has the effect of reducing the coloration of the sample. When element B contains a rare earth element, element A does not necessarily contain a rare earth element.

[0021] Ceramic material 10A x BO ｚ In the formula, the ratio of the amount of rare earth elements (rare earth elements located at the A site) contained in element A to the total amount of each element A (each element located at the A site) (amount of rare earth elements / total amount of element A) is preferably 0% or more and 3.0% or less, more preferably 0.1% or more and 2.0% or less, even more preferably 0.2% or more and 1.5% or less, even more preferably 0.2% or more and 1.3% or less, even more preferably 0.3% or more and 1.3% or less, even more preferably 0.3% or more and 1.0% or less, even more preferably 0.4% or more and 1.0% or less, and even more preferably 0.5% or more and 0.9% or less, by molar ratio. When the amount of rare earth elements contained in the A site is within this range, visible light can be appropriately refracted and transmitted. Note that, when element A contains multiple rare earth elements, the amount of rare earth elements contained in element A refers to the total amount of these rare earth elements.

[0022] (Other components) Ceramic material 10 A x BO ｚIn the formula (1), the element A may contain an element other than an alkaline earth metal element and a rare earth element as another component (adjuster), such as at least one of Na, K, and Bi.

[0023] (Element B) (Main component) A x BO ｚ In the formula (1), B is an element located at the B site in the perovskite structure. In the first embodiment, the element B is mainly composed of Ti. That is, it can be said that the main component of the elements located at the B site (the element with the highest content among the elements located at the B site) is Ti.

[0024] Ceramic material 10A x BO ｚ In the formula, the ratio of the amount of Ti contained in element B (Ti located at the B site) to the total amount of each element B (each element located at the B site) (amount of Ti / total amount of element B) is 70% or more, preferably 80% or more, more preferably 90% or more and 99.9% or less, and even more preferably 97% or more and 99.8% or less, by molar ratio. When the amount of Ti contained in the B site is within this range, it becomes possible to transmit visible light while appropriately refracting it.

[0025] (Rare Earth Element) Element B preferably contains a rare earth element as a substitution component (subcomponent). The rare earth element contained in element B is preferably at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and is preferably at least one of La, Sm, Eu, Gd, Tb, Ho, Yb, and Lu, and more preferably Sm, Gd, Tb, Yb, and Lu. By including such a rare earth element in element B, it is possible to improve sinterability and transmit visible light while appropriately refracting it. In addition, by including a rare earth element in element B, vacancy defects occurring at the position in the crystal lattice of element A, or the position in the crystal lattice of element B, or at oxygen positions, or element defects accompanying light absorption occurring at the crystal particle interface, impurities such as adjusters, etc. are balanced in a charge-neutral relationship, which also has the effect of reducing the coloration of the sample. When element A contains a rare earth element, element B does not necessarily contain a rare earth element.

[0026] Ceramic material 10A x BO ｚ In the formula (I), the ratio of the amount of rare earth elements contained in element B (rare earth elements located at the B site) to the total amount of each element B (each element located at the B site) (amount of rare earth elements / total amount of element B) is preferably 0% or more and 3.0% or less, more preferably 0% or more and 2.0% or less, even more preferably 0% or more and 1.0% or less, even more preferably 0% or more and 0.8% or less, even more preferably 0% or more and 0.5% or less, and even more preferably 0% or more and 0.3% or less, in molar ratio. When the amount of rare earth elements contained in the B site is within this range, visible light can be appropriately refracted and transmitted. Note that the ratio of the amount of rare earth elements contained in element B to the total amount of each element B (amount of rare earth elements / total amount of element B) may be greater than 0% in molar ratio. Note that, when element B contains multiple rare earth elements, the amount of rare earth elements contained in element B refers to the total amount of these rare earth elements.

[0027] (Other components) Ceramic material 10 A x BO ｚIn the formula (I), the element B may contain an element other than an alkaline earth metal element and a rare earth element as another component (adjuster), such as at least one of Zr, Ge, Zn, Sc, Y, Ga, Si, Sn, Nb, Ta, Hf, and Al.

[0028] A x BO ｚ With regard to the rare earth elements contained in A and B in the formula (I), the sum of the ratio of the amount of rare earth elements contained in element A (rare earth elements located at the A site) (amount of rare earth elements / total amount of element A) to the ratio of the amount of rare earth elements contained in element B (rare earth elements located at the B site) (amount of rare earth elements / total amount of element B) is preferably 0% to 3.0% in molar ratio, more preferably 0% to 2.0%, even more preferably 0% to 1.0%, still more preferably 0% to 0.8%, even more preferably 0% to 0.5%, and still more preferably 0% to 0.3%. Note that the sum of the ratio of the amount of rare earth elements contained in element A (amount of rare earth elements / total amount of element A) to the ratio of the amount of rare earth elements contained in element B (amount of rare earth elements / total amount of element B) in molar ratio may be greater than 0%.

[0029] (Number x) A of ceramic material 10 x BO ｚ In the formula, x is a numerical value indicating the ratio (molar ratio) of the content of element A, more specifically, the molar ratio of the content of element A to the content of element B. Here, when element A contains multiple elements, the content of element A refers to the total content of those elements, and similarly, when element B contains multiple elements, the content of element B refers to the total content of those elements.

[0030] The numerical value x is 0.9 or more and 1.0 or less, preferably 0.95 or more and 0.999 or less, more preferably 0.98 or more and 0.999 or less, and still more preferably 0.98 or more and 0.998 or less. When the numerical value x is in this range, an appropriate crystal structure can be obtained.

[0031] (Number z) A of ceramic material 10 x BOｚ In the formula, z is a numerical value indicating the content (molar ratio) of O, more specifically, the molar ratio of the content of O to the content of element B. x BO ｚ This is a value that ensures overall charge neutrality, and may be, for example, 3.

[0032] (Subcomponent) The ceramic material 10 contains the above-mentioned main component A. x BO ｚ The ceramic material 10 may contain a secondary component other than the above. The ceramic material 10 preferably contains at least one selected from Li, Si, B, Y, Al, Ca, and Mg as a secondary component, and more preferably contains Si. This secondary component is derived from a sintering aid used when sintering the raw materials to produce the ceramic material 10. The ceramic material 10 may contain the secondary component in the form of an oxide or carbonate of the above-listed elements. The content of this secondary component is preferably 50 ppm to 50,000 ppm, more preferably 50 ppm to 20,000 ppm, and even more preferably 50 ppm to 5,000 ppm, by mass relative to the entire ceramic material 10. By setting the content of the secondary component within this range, a ceramic material 10 with a high refractive index and high transmittance can be appropriately produced. The content of the secondary component can be measured by inductively coupled plasma mass spectrometry (ICP-MS).

[0033] The ceramic material 10 may also contain auxiliary components other than those derived from the sintering aid. If the auxiliary components other than those derived from the sintering aid are referred to as auxiliary components, the ceramic material 10 preferably contains at least one selected from Ce and Pr as the auxiliary component. By including such an auxiliary component, the auxiliary component functions as an oxidizing agent, appropriately accepting electrons and more effectively suppressing a decrease in transmittance. The ceramic material 10 may also contain the auxiliary component in the form of an oxide of the above-listed element. The content of the auxiliary component is preferably 50 ppm to 50,000 ppm, more preferably 50 ppm to 20,000 ppm, and even more preferably 50 ppm to 5,000 ppm, by mass relative to the entire ceramic material 10. By setting the content of the auxiliary component within this range, a ceramic material 10 with a high refractive index and high transmittance can be appropriately produced. The content of the auxiliary component can also be measured by inductively coupled plasma mass spectrometry (ICP-MS).

[0034] In addition to the above-described main component, subcomponent, and auxiliary component, the ceramic material 10 may contain any component as an inevitable impurity. It is preferable that the ceramic material 10 does not contain any component other than the main component, subcomponent, and auxiliary component, except for the inevitable impurities.

[0035] (Characteristics of Ceramic Material) Next, the characteristics of the ceramic material 10 will be described.

[0036] (Refractive Index) The refractive index of the ceramic material 10 for light with a wavelength of 635 nm is preferably 2.30 or more, more preferably 2.30 to 2.45, more preferably 2.34 or more, more preferably 2.35 to 2.45, and even more preferably 2.36 to 2.43. By having the refractive index within this range, the internal strain of the material can be reduced, maintaining optical quality and allowing visible light to be appropriately refracted. The refractive index can be measured by spectroscopic ellipsometry (JA Woollam Co., Inc.; M-2000 DI).

[0037] (Transmittance) The ceramic material 10 preferably has a total light transmittance of 10% or more at a thickness of 1 mm for light with a wavelength of 635 nm, more preferably 15% or more, more preferably 20% or more, more preferably 25% or more, more preferably 30% or more, and even more preferably 40% or more. The total light transmittance at a thickness of 1 mm can be measured by attaching the ceramic material 10 to an integrating sphere using an integrating sphere unit (150 mm InGaAs Int. Sptere) as a detector in a spectrophotometer (manufactured by PerkinElmer; LAMBDA950). In addition, if the actual thickness of the ceramic material 10 is not 1 mm, the measured value can be converted to the total light transmittance per mm thickness using the Lambert-Beer law. Furthermore, if the plate thickness t is greater than 1 mm, the plate thickness of the ceramic material 10 may be adjusted to 1 mm by polishing, etching, or the like before measurement. The total light transmittance is determined depending on the composition of the ceramic material 10, but even if the composition is the same, it may vary depending on the production process of the ceramic material 10. Therefore, for example, the total light transmittance can be set within the above range by appropriately adjusting the production process of the ceramic material 10. Note that the method for adjusting the production process here can be a known method, such as carefully mixing the raw materials or appropriately adjusting the sintering conditions.

[0038] The ceramic material 10 may be colored, in other words, may be visually recognized as a predetermined color other than colorless when irradiated with sunlight.

[0039] (Average particle size) A, a compound with a perovskite structure, of the ceramic material 10 x BO ｚThe average particle size of each particle is preferably 2 μm or more and 100 μm or less, more preferably 2 μm or more and 80 μm or less, and even more preferably 2 μm or more and 50 μm or less. Having an average particle size within this range enables visible light to be appropriately refracted while being transmitted. The average particle size here can be measured as follows. The surface of the ceramic material 10 is mirror-polished with a grinding stone having a grain size number of #30000 as specified in JIS R6001, and the mirror-polished ceramic material is heat-treated for 30 minutes at (sintering temperature -100) ° C (or 1350 ° C if the sintering temperature is unknown). Ten images of the surface of the heat-treated ceramic material 10 are taken using a scanning electron microscope (SEM) at an appropriate magnification (for example, a magnification that captures 10 to 50 particles (the entire particle area) within the imaging range), and the area of ​​all particles included in each image is measured. Then, the diameter of the particle is calculated from the area of ​​the particle, assuming that the particle is circular. The calculated diameter is taken as the particle size of the particle, and the average value of the particle size is taken as the average particle size.

[0040] (Number of pores) 1 mm of ceramic material 10 ３ The number of pores with a radius of 5 μm or more per unit area is preferably 0 to 520, more preferably 0 to 50, and even more preferably 0 to 10. By having the number of pores in this range, it is possible to transmit visible light while appropriately refracting it. The number of pores here can be measured as follows. That is, the center of the ceramic material 10 is cut out to a size of 1 mm length x 1 mm width x 10 mm height, and a cross section perpendicular to the height direction is measured using X-ray Computer Tomography (X-ray CT) with a voxel of 1.7 μm using Bruker's SkyScan 2214, and a single-layer cross-sectional view is obtained using Bruker's NRecon. Then, while shifting the imaging height, the obtained three-dimensional image is analyzed using Bruker's CTAN, and the number of pores with a radius of 5 μm or more obtained is counted by 1 mm. ３ This is converted to the number of pores per unit area.

[0041] (Method for manufacturing ceramic material) The ceramic material 10 according to this embodiment may be manufactured by any method, but is preferably manufactured by a solid-phase method (solid-phase reaction method), and an example of the manufacturing method will be described below.

[0042] (Preparation of Raw Materials) In this manufacturing method, a powdered main raw material that is the raw material of the main component of the ceramic material 10 is prepared as the raw material used to manufacture the ceramic material 10. The main raw material is a material that contains an element contained in the main component of the ceramic material 10. The main raw material may be any material that contains an element contained in the main component of the ceramic material 10. The main raw material may be, for example, the main component of the ceramic material 10 itself. That is, for example, in this embodiment, the main raw material is AxBO ｚ Alternatively, the main raw material may be a powder of element A. The main raw material may also be a plurality of types of materials containing some of the elements contained in the main components of the ceramic material 10. That is, for example, in this embodiment, the main raw material may be an oxide or carbonate of element A and an oxide of element B.

[0043] When the ceramic material 10 contains a minor component, a powdered minor component that is the raw material of the minor component of the ceramic material 10 is also prepared. The minor component is a material containing an element contained in the minor component of the ceramic material 10, and is a so-called sintering aid. The minor component may be any material containing an element contained in the minor component of the ceramic material 10. The minor component may be an oxide of an element contained in the minor component (for example, Li ２ O, SiO ２ , B ２ O ３ , MgO, etc.), fluorides of elements contained in the secondary components (e.g., LiF, MgF ２ etc.), carbonates of elements contained in the secondary components (e.g., Li ２ CO ３ etc.)

[0044] When the ceramic material 10 contains an auxiliary component, a powdered auxiliary raw material that is the raw material for the auxiliary component of the ceramic material 10 is also prepared. The auxiliary raw material is a material that contains an element contained in the auxiliary component of the ceramic material 10, and is a so-called oxidizer. The auxiliary raw material may be any material that contains an element contained in the auxiliary component of the ceramic material 10. The auxiliary raw material may be an oxide of the element contained in the auxiliary component (e.g., CeO ２ , Pr ６ O １１ etc.)

[0045] The average particle size of the raw materials (main raw material, sub-raw material, and auxiliary raw material) may be any value, but is preferably, for example, 0.03 μm or more and 5.00 μm or less. This allows for proper sintering. The average particle size of the raw materials can be measured, for example, using a particle size distribution measuring device (Shimadzu Corporation: SALD-2300).

[0046] The types and compounding ratios of the raw materials may be appropriately set depending on the composition of the ceramic material 10 to be produced.

[0047] (Mixing of Raw Materials) Next, the prepared raw materials are mixed. Any method for mixing the raw materials may be used, for example, a ball mill. Alternatively, a solvent may be added to the raw materials to perform wet mixing. In this case, for example, a solvent (e.g., water or ethanol) and a mixing medium (e.g., alumina or zirconia) may be added to the raw materials, and the mixture may be wet-mixed for a period of 1 hour to 5 hours. A dispersant may also be added to disperse the raw material powders. After wet mixing, once mixing is complete, liquid components are removed from the mixed raw materials (slurry) by a drying process or the like. The raw material powder may contain impurities of 500 wtppm or less due to the alumina and zirconia mixing medium. If the mixed raw materials contain carbon components, a carbon removal process may be performed to remove the carbon components. The carbon removal process may involve, for example, holding the mixed raw materials at a temperature ranging from 800°C to 1100°C for 1 hour to 20 hours. The carbon removal treatment may be carried out in an air atmosphere or an oxygen atmosphere.

[0048] (Shaping of raw materials) Next, the mixed raw materials are molded into a desired shape to obtain a molded body, which is an assembly of raw materials molded into a desired shape. The method for manufacturing the molded body is not particularly limited, but molding by powder compact molding or slip casting is preferred.

[0049] (Powder Compaction Method) In the powder compaction method, for example, a binder (e.g., an organic binder such as polyvinyl alcohol) may be added to the mixed raw materials. Alternatively, a raw material slurry may be obtained by adding a binder to the raw materials. Note that, in addition to the binder, an organometallic compound or a lactate component may also be added. The obtained raw material slurry is then pressurized and molded into a desired shape. For example, the raw material slurry is molded using a uniaxial processing press, and then subjected to a CIP (Cold Isostatic Pressing) process under conditions of 125 MPa or more and 175 MPa or less to obtain a molded body.

[0050] (Slip Casting Method) For example, a molded body can also be produced by a slip casting method. Slip casting methods include flow casting, pressure casting, and drain casting. Pressure casting is a method in which raw material slurry is poured into a stack of molds (e.g., plaster) under pressure from below, and the raw material slurry is dried without being discarded. The raw material slurry can be obtained by a method similar to that described for the powder compact molding method. The drain casting method is a method in which a mixed raw material slurry is poured into a casting mold and the solvent is dried to obtain a molded body. The raw material slurry is obtained by adding a solvent to the mixed raw materials. The solvent may be aqueous or non-aqueous. However, if the solvent is aqueous, a plaster mold, which is commonly used as a slip casting mold, may dissolve water in the plaster and become mixed into the molded body, potentially degrading the optical properties. Therefore, a resin mold or porous ceramic mold is preferably used. When a non-aqueous solvent such as alcohol is used as a solvent, a plaster mold is preferably used. In this embodiment, an aqueous solvent is preferably used. The mold is preferably made of porous ceramics, and the mold wall may be made of mirror-finished glass or PVC to improve mold releasability.

[0051] (Degreasing of compact) Next, a degreasing treatment is performed to remove binder components, if any, from the compact. In the degreasing treatment, for example, the obtained compact is heated to 700°C or higher and 800°C or lower in the air atmosphere.

[0052] (Sintering of the molded body) Next, the degreased molded body is sintered to obtain a ceramic material 10, which is a sintered body of the molded body (raw material). In the sintering process, the molded body is heat-treated in an oxygen atmosphere. In this heat treatment, it is preferable to heat the molded body while pressurizing it. For example, the pressure applied to the molded body may be 1 atm or more and 3 atm or less, the heating temperature of the molded body may be 1300°C or more and 1550°C or less, and the pressurizing and heating time may be more than 0 hours and less than 24 hours. The pressurizing and heating time is more preferably more than 1 hour and less than 24 hours. In addition, in the sintering process, after the heat treatment in the oxygen atmosphere, a HIP (Hot Isostatic Pressing) process may be performed in an atmosphere containing Ar (for example, an Ar atmosphere or a mixed atmosphere of Ar and oxygen). The applied pressure in the HIP treatment may be 100 MPa or more and 200 MPa or less, the heating temperature may be 1250°C or more and 1450°C or less, and the HIP treatment time may be 1 hour or more and 4 hours or less. In addition, a post-annealing treatment may be performed on the sintered body after the HIP treatment, in which the sintered body is held at 800°C or more and 1400°C or less in an air atmosphere or an oxygen atmosphere. This makes it possible to recover the reduced state caused by the HIP treatment.

[0053] The ceramic material 10 obtained by sintering in this manner may be subjected to mechanical processing such as polishing.

[0054] In this way, by using the solid-phase method and sintering in an oxygen atmosphere, it is possible to appropriately manufacture a ceramic sintered body that can refract and transmit visible light. Furthermore, by using the sintering conditions shown above, it is possible to more appropriately manufacture a ceramic sintered body that can refract and transmit visible light.

[0055] (Effects) As described above, the ceramic material 10 according to the first aspect of the present disclosure has A x BO ｚwherein element A is an alkaline earth metal element as a main component, element B is Ti as a main component, at least one of element A and element B contains a rare earth element, x is 0.9 or more and 1.0 or less, z is a value that establishes charge neutrality in the entire chemical formula, and the total light transmittance at a thickness of 1 mm for light with a wavelength of 635 nm is 10% or more.

[0056] As a result of extensive research, the inventors have found that, for example, when Ti is included in the B site, a high refractive index can be achieved by the Ti, but Ti is easily reduced during sintering, which may result in coloration and reduced transmittance. Furthermore, the inventors have found that, for example, when only an alkaline earth metal is included in the A site, defects are not generated, making it difficult for atoms to migrate and preventing the formation of a dense body. In contrast, as a result of extensive research, the inventors have found that by partially substituting a rare earth element for at least one of the A site and the B site, sinterability can be improved, transmittance reduction can be suppressed, and a high refractive index and high transmittance can be ensured. That is, as in this embodiment, by using an alkaline earth metal as the main component of the A site and Ti as the main component of the B site, and substituting a rare earth element for at least one of the A site and the B site, visible light can be appropriately refracted while being transmitted.

[0057] The ceramic material 10 according to the second aspect of the present disclosure is the ceramic material 10 according to the first aspect, wherein x is preferably 0.98 to 0.999. By setting x in this range, visible light can be appropriately refracted and transmitted.

[0058] A ceramic material 10 according to a third aspect of the present disclosure is the ceramic material 10 according to the first or second aspect, wherein element A includes a rare earth element, and the ratio of the amount of the rare earth element contained in element A to the total amount of each element contained in element A is preferably 0% or more and 3% or less in molar ratio. By setting the content of the rare earth element in the A site within this range, visible light can be transmitted while being appropriately refracted.

[0059] A ceramic material 10 according to a fourth aspect of the present disclosure is the ceramic material 10 according to any one of the first to third aspects, wherein A contains Sr and preferably contains at least one of Ca and Ba. By containing such an element in the A site, visible light can be transmitted while being appropriately refracted.

[0060] A ceramic material 10 according to a fifth aspect of the present disclosure is the ceramic material 10 according to any one of the first to fourth aspects, wherein A contains a rare earth element, and the ratio of the amount of the rare earth element contained in A to the total amount of each element contained in A is preferably 0.5% or more and 0.9% or less by molar ratio. By containing a rare earth element in the A site in this manner, visible light can be transmitted while being appropriately refracted.

[0061] A ceramic material 10 according to a sixth aspect of the present disclosure is the ceramic material 10 according to any one of the first to fifth aspects, wherein the ratio of the amount of alkaline earth metal element contained in A to the total amount of each element contained in A is preferably 90% or more and 99.5% or less in molar ratio. By including an alkaline earth metal element in element A in this manner, visible light can be transmitted while being appropriately refracted.

[0062] A ceramic material 10 according to a seventh aspect of the present disclosure is the ceramic material 10 according to any one of the first to sixth aspects, wherein element B includes a rare earth element, and the ratio of the amount of the rare earth element contained in element B to the total amount of each element contained in element B is preferably 0% or more and 3% or less in molar ratio. By setting the content of the rare earth element in the B site within this range, visible light can be transmitted while being appropriately refracted.

[0063] The ceramic material 10 according to an eighth aspect of the present disclosure is the ceramic material 10 according to any one of the first to seventh aspects, and preferably has a molar ratio of Ti contained in element B of 90% to 99.9%. By setting the content of Ti in the B site within this range, visible light can be transmitted while being appropriately refracted.

[0064] The ceramic material 10 according to a ninth aspect of the present disclosure is the ceramic material 10 according to any one of the first to eighth aspects, and preferably has a refractive index of 2.34 or more for light with a wavelength of 635 nm, thereby enabling appropriate refraction of visible light.

[0065] The ceramic material 10 according to a tenth aspect of the present disclosure is the ceramic material 10 according to any one of the first to ninth aspects, and preferably has a refractive index of 2.35 or more and 2.45 or less for light with a wavelength of 635 nm, thereby enabling appropriate refraction of visible light.

[0066] The ceramic material 10 according to an eleventh aspect of the present disclosure is the ceramic material 10 according to any one of the first to tenth aspects, and preferably has a total light transmittance of 25% or more at a thickness of 1 mm for light with a wavelength of 635 nm, thereby enabling appropriate refraction of visible light.

[0067] The ceramic material 10 according to a twelfth aspect of the present disclosure is the ceramic material 10 according to any one of the first to eleventh aspects, wherein the ceramic material 10 comprises a compound having a perovskite structure (A x BO ｚ ) preferably has an average particle size of 2 μm or more and 100 μm or less, which allows visible light to be transmitted while being appropriately refracted.

[0068] The ceramic material 10 according to a thirteenth aspect of the present disclosure is the ceramic material 10 according to any one of the first to twelfth aspects, comprising a compound having a perovskite structure (A x BO ｚ ) preferably has an average particle size of 2 μm or more and 50 μm or less, which allows visible light to be transmitted while being appropriately refracted.

[0069] The ceramic material 10 according to a fourteenth aspect of the present disclosure is the ceramic material 10 according to any one of the first to thirteenth aspects, ３ It is preferable that the number of pores with a radius of 5 μm or more per unit area is 0 to 520. This allows visible light to be transmitted while being appropriately refracted.

[0070] An optical member according to a fifteenth aspect of the present disclosure includes the ceramic material 10 according to any one of the first to fourteenth aspects as a light guide plate. According to the present disclosure, visible light can be transmitted while being appropriately refracted.

[0071] A head-mounted display according to a sixteenth aspect of the present disclosure includes a light guide plate member made of the ceramic material 10 according to any one of the first to fourteenth aspects. According to the present disclosure, visible light can be transmitted while being appropriately refracted.

[0072] A manufacturing method according to a seventeenth aspect of the present disclosure is a manufacturing method of the ceramic material 10 according to any one of the first to fourteenth aspects, and includes mixing solid raw materials, shaping the mixed raw materials to obtain a molded body, and sintering the molded body in an oxygen atmosphere to obtain a ceramic material. According to the present disclosure, visible light can be transmitted while being appropriately refracted.

[0073] A manufacturing method according to an eighteenth aspect of the present disclosure is a manufacturing method of the ceramic material 10 according to the seventeenth aspect, which is manufactured by a solid-state reaction method. According to the present disclosure, it is possible to manufacture the ceramic material 10 that can transmit visible light while appropriately refracting it.

[0074] A manufacturing method according to a 19th aspect of the present disclosure is a manufacturing method of ceramic material 10 according to the 17th or 18th aspect, in which a ceramic material is manufactured by heating a molded body while pressurizing it in an oxygen atmosphere, the pressure applied to the molded body is 1 atm or more and 3 atm or less, the heating temperature of the molded body is 1300°C or more and 1550°C or less, and the pressurizing and heating time is more than 1 hour and 24 hours or less. According to the present disclosure, ceramic material 10 that can transmit visible light while appropriately refracting it can be manufactured.

[0075] A manufacturing method according to a twentieth aspect of the present disclosure is a manufacturing method of the ceramic material 10 according to any one of the seventeenth to nineteenth aspects, in which a compact is heated under pressure and then subjected to HIP treatment in an Ar-containing atmosphere, the applied pressure in the HIP treatment being 100 MPa or more and 200 MPa or less, the heating temperature in the HIP treatment being 1250°C or more and 1450°C or less, and the HIP treatment time being 1 hour or more and 4 hours or less. According to the present disclosure, it is possible to manufacture the ceramic material 10 that can transmit visible light while appropriately refracting it.

[0076] Examples Next, examples will be described. Note that the embodiment may be modified as long as the effects of the invention are achieved. Tables 1 and 2 show the ceramic materials of each example and the evaluation results thereof.

[0077]

[0078] (Example 1) In Example 1, strontium carbonate, titanium oxide, samarium oxide, and ytterbium oxide powders were prepared as main raw materials. Each main raw material was prepared in a stoichiometric ratio of Sr ０．９９５ Sm ０．００５ Ti ０．９９５ Yb ０．００５ O ３ The blending ratio was set so that the average particle size of the raw materials was 0.1 to 2.0 μm. The raw materials were wet-mixed using a particle size distribution analyzer (Shimadzu Corporation: SALD-2300) under ball mill mixing conditions for 2 hours using alumina balls as grinding media, and then the mixed raw materials were dried at 80°C for 10 hours. The dried raw materials were then subjected to carbon removal treatment at 900°C for 10 hours. A binder (aqueous PVA solution, prepared raw materials from Kanto Chemical Co., Inc.) was added to the raw materials after carbon removal treatment to obtain a raw material slurry. The obtained raw material slurry was dried at 80°C for 10 hours, and a molded body was obtained using a uniaxial press and a CIP method. The molded body was sintered at 1450°C under 2 atm of oxygen to obtain a ceramic material. The ceramic material of Example 1 has the chemical formula Sr ０．９９５ Sm ０．００５ Ti ０．９９５ Yb ０．００５ O ３The result was a sintered body of a crystal with a perovskite structure, with a composition expressed as follows: The main component of the A site is Sr, the minor component of the A site is Sm, the main component of the B site is Ti, and the minor component of the B site is Yb.

[0079] The transmittance (total light transmittance at 1 mm thickness) and refractive index of the ceramic material of Example 1 for light with a wavelength of 635 nm, the average particle size, and ３ The number of pores with a radius of 5 μm or more per unit area was measured. The measurement conditions were the same as those described in this embodiment. The measurement results are shown in Table 1.

[0080] (Examples 2 to 50) In Examples 2 to 48, ceramic materials were produced in the same manner as in Example 1, except that the compositions were those shown in Tables 1 and 2. In Example 49, a ceramic material was produced in the same manner as in Example 1, except that the composition was that shown in Table 2 and the atmosphere during sintering was air instead of oxygen. In Example 50, a ceramic material was produced in the same manner as in Example 1, except that the composition was that shown in Table 2, the atmosphere during sintering was air instead of oxygen, and SPS (spark plasma sintering) was used instead of the solid-state method. The measurement results for each example are shown in Tables 1 and 2.

[0081] (Evaluation) The optical properties of the ceramic materials of each example were evaluated. In the evaluation of optical properties, transparent graph paper was placed on a high-intensity light, and when a sample was placed on it, if the light was appropriately refracted and visible, it was judged as passing, and if not, it was judged as failing.

[0082] As shown in Tables 1 and 2, Examples 1 to 46, which are examples containing a rare earth element in at least one of the A site and the B site, passed the evaluation of optical properties, indicating that visible light can be transmitted while being appropriately refracted. On the other hand, Examples 47 and 48, which are comparative examples not containing a rare earth element, failed the evaluation of optical properties, indicating that visible light cannot be transmitted while being appropriately refracted. Furthermore, Examples 49 to 50, which contain a rare earth element but have low transmittance, failed the evaluation of optical properties, indicating that visible light cannot be transmitted while being appropriately refracted.

[0083] Although the embodiments of the present disclosure have been described above, the embodiments are not limited to the contents of these embodiments. Furthermore, the above-described components include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the above-described components can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the spirit of the above-described embodiments.

[0084] 10. Ceramic materials

Claims

1. A x BO ｚ a ceramic material having as its main component a compound with a perovskite structure represented by the chemical formula: wherein A is mainly composed of an alkaline earth metal element, B is mainly composed of Ti, at least one of A and B contains a rare earth element, x is 0.9 or more and 1.0 or less, and z is a value that satisfies charge neutrality of the entire chemical formula, and the ceramic material has a total light transmittance of 10% or more for light with a wavelength of 635 nm at a thickness of 1 mm.

2. The ceramic material according to claim 1, wherein x is 0.98 or more and 0.999 or less.

3. The ceramic material according to claim 1, wherein A contains a rare earth element, and the ratio of the amount of the rare earth element contained in A to the total amount of each element contained in A is, in molar ratio, 0% or more and 3% or less.

4. The ceramic material according to claim 1, wherein A contains Sr and at least one of Ca and Ba.

5. The ceramic material according to claim 1, wherein A contains a rare earth element, and the ratio of the amount of the rare earth element contained in A to the total amount of each element contained in A is 0.5% or more and 0.9% or less in molar ratio.

6. The ceramic material according to claim 1, wherein the ratio of the amount of alkaline earth metal element contained in A to the total amount of each element contained in A is 90% or more and 99.5% or less in molar ratio.

7. The ceramic material according to claim 1, wherein B contains a rare earth element, and the ratio of the amount of the rare earth element contained in B to the total amount of each element contained in B is, in molar ratio, 0% or more and 3% or less.

8. The ceramic material according to claim 1, wherein the amount of Ti contained in element B is 90% or more and 99.9% or less in molar ratio.

9. The ceramic material according to claim 1, which has a refractive index of 2.34 or more for light with a wavelength of 635 nm.

10. The ceramic material according to claim 9, having a refractive index of 2.35 or more and 2.45 or less for light with a wavelength of 635 nm.

11. The ceramic material according to claim 1, wherein the total light transmittance for light with a wavelength of 635 nm through a thickness of 1 mm is 25% or more.

12. The ceramic material according to claim 1, wherein the compound having a perovskite structure has an average particle size of 2 μm or more and 100 μm or less.

13. The ceramic material according to claim 1, wherein the compound having a perovskite structure has an average particle size of 2 μm or more and 50 μm or less.

14. 1 mm ３ The ceramic material according to claim 1, wherein the number of pores having a radius of 5 μm or more per unit area is 0 to 520.

15. An optical component comprising a light guide plate made of the ceramic material according to any one of claims 1 to 14.

16. A head-mounted display, comprising a light guide plate member made of the ceramic material according to any one of claims 1 to 14.

17. A method for producing a ceramic material according to any one of claims 1 to 14, comprising: mixing solid raw materials; shaping the mixed raw materials to obtain a molded body; and sintering the molded body in an oxygen atmosphere to obtain the ceramic material.

18. A method for producing the ceramic material according to claim 17, which is produced by a solid-state reaction method.

19. A method for producing a ceramic material as described in claim 17, wherein the ceramic material is produced by heating the molded body while pressurizing it in an oxygen atmosphere, the pressure applied to the molded body is 1 atm or more and 3 atm or less, the heating temperature of the molded body is 1300°C or more and 1550°C or less, and the pressurizing and heating time is more than 1 hour and 24 hours or less.

20. A method for producing a ceramic material as described in claim 19, wherein the compact is heated under pressure and then subjected to HIP treatment in an atmosphere containing Ar, the applied pressure in the HIP treatment being 100 MPa or more and 200 MPa or less, the heating temperature in the HIP treatment being 1250°C or more and 1450°C or less, and the time period for the HIP treatment being 1 hour or more and 4 hours or less.

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