Ion extraction compound and its manufacturing method

Abstract

To provide an ion extraction compound using an II type IV group clathrate compound and NaAlB14, etc., as a starting material; an ion substitute, such as acid hydride using an oxide as a starting material; an intercalation compound using a compound having a van der Waals gap as a starting material; and methods for easily manufacturing them.SOLUTION: Na ions 11 are extracted from an II type IV group clathrate compound including Na ion by contacting a Na ion conductor 20 to the II type IV group clathrate compound and heating the II type IV group clathrate compound while applying a positive voltage V to the Na ion conductor 20. Na ion extraction NaAlB14, acid hydride, an intercalation compound, etc., are manufactured by performing voltage application and heating in high pressure using NaAlB14, an oxide and a compound having a van der Waals gap, etc., as a starting material to perform electrochemical treatment.SELECTED DRAWING: Figure 2B

Description

[Technical Field]

[0001] The present invention relates to an ion extraction compound and a method for producing the same, an ion substitution compound and a method for producing the same, an intercalation compound and a method for producing the same, and a pressure cell for high-pressure solid-state electrochemistry, and + ) removed from type II Si clathrate compounds and NaAlB 14 The present invention is suitable for application to various ion-extracting compounds such as those mentioned above, various ion-substituted compounds in which ions have been substituted, and various intercalation compounds containing metal ions. [Background technology]

[0002] Clathrate compounds have a cage-like structure in which ions are encapsulated. Clathrate compounds are known to have low thermal conductivity due to the rattling effect resulting from this structure. Clathrate compounds based on Si as the cage structure include Si clathrate compounds and Si-Ge clathrate compounds. The electronic properties of these clathrate compounds can be modulated by removing Na ions from the cage structure. The removal of Na ions is expected to lead to a variety of functionalities, including photoelectric conversion materials for solar power generation, thermoelectric conversion materials, electrode materials for ion batteries that utilize the voids left after the removal of Na ions, and storage materials for hydrogen gas. Regarding solar power generation, removing some or all of the Na ions from the cage structure of Si clathrate compounds and Si-Ge clathrate compounds results in direct transition semiconductors with a band gap of 1.3–1.8 eV. This is expected to dramatically improve energy conversion efficiency compared to the indirect transition semiconductor Si used in conventional solar power generation. In fact, when comparing the absorption coefficients of Si, an indirect transition semiconductor, and Si clathrate compounds, a direct transition semiconductor, it has been reported that the absorption coefficient of Si clathrate compounds is extremely large in the range of 2.3 to 3.3 eV. Furthermore, as mentioned above, clathrate compounds are advantageous as thermoelectric conversion materials due to their low thermal conductivity. Furthermore, by adjusting the concentration of Na ions within the cage structure by removing Na ions, it is possible to appropriately adjust the electronic conductivity. For this reason, clathrate compounds are expected to be used as high-performance thermoelectric conversion materials. Furthermore, as electrode materials for ion batteries and storage materials for hydrogen gas, etc., the voids formed by removing Na ions from Si clathrate compounds may function as adsorption sites for gases and other ionic species, and thus are expected to be useful.

[0003] It has been known that Na ions can be extracted from Si clathrate compounds by vacuum annealing if the Si clathrate compound is microcrystalline (see Non-Patent Document 1). Meanwhile, in recent years, it has become possible to grow large Si clathrate compound single crystals measuring several millimeters or more. However, according to the inventors' unique findings, even vacuum annealing of such very large Si clathrate compound single crystals does not remove Na ions located more than 200 μm deep from the surface. Even if vacuum annealing is performed for a long time, the region from which Na ions can be extracted is limited to approximately 200 μm from the surface. Furthermore, Na volatilized from the Si clathrate compound single crystals by vacuum annealing forms impurities such as Na2CO3 on the crystal surface. Therefore, in order to use Si clathrate compounds in the various technologies mentioned above, a method for extracting Na ions compatible with the increasing size of Si clathrate compound single crystals must be established. In particular, a new method based on a novel idea is essential for extracting Na ions from large Si clathrate compound single crystals, but no such method has been proposed to date.

[0004] Meanwhile, electrochemistry has traditionally been used to synthesize a variety of inorganic compounds, but in most cases, a liquid-phase process is used. However, in liquid-phase processes, synthesis conditions are limited to low temperatures and low voltages due to solvent evaporation and electrolysis. On the other hand, in liquid-phase processes, it is difficult to electrically promote ion diffusion, except for materials with extremely high ion conductivity, due to volume changes and scattering at interfaces associated with ion diffusion. Even so, some research has been conducted on amorphous materials such as glass. For example, with the aim of developing fuel cells, phosphate glass is heated to around 300-400°C and a voltage is applied to convert the Na ions in the glass into protons (H +) has been reported (see Non-Patent Document 2). Such amorphous materials flexibly change shape above their softening point, maintaining a good solid-solid interface and reducing volume changes and void formation associated with atomic migration. In contrast, the solid-solid interface of crystalline materials is not suitable for the migration of atoms or ions because many gaps exist on a microscale. This is thought to be the reason why solid-state electrochemistry has not yet penetrated the synthesis of inorganic polycrystals, with the exception of some highly ionic conductors.

[0005] Furthermore, hydrogen is a highly permeable gas at atmospheric pressure, making the synthesis of inorganic compounds containing hydrogen atoms generally difficult. For example, as of 2018, only 50 examples of the synthesis of oxyhydrides had been reported (see Non-Patent Document 3). However, hydrogen has recently attracted global attention as a clean energy source, and the development of technologies and materials that can utilize it is required. To synthesize novel oxyhydrides that can utilize hydrogen in this way, simple annealing under a hydrogen atmosphere has its limitations, and a new synthesis process based on a new mechanism is required. Conventionally, a known method for synthesizing perovskite oxyhydrides based on perovskite oxides involves mixing and sealing a hydrogen source such as CaH2 or LaH3 with the sample and sintering it at low temperatures. However, due to the low-temperature synthesis, this method makes it difficult to increase the sintered density, and the weak bonding between particles affects the physical properties. Furthermore, high-temperature annealing after hydrogen introduction results in the release of hydrogen from the sample. For example, compounds such as ATiO3 (A = Ba, Ca, Sr) require high-temperature sintering at around 1200°C to sufficiently reduce scattering at grain boundaries, but because hydrogen is released at 400 to 500°C, it is difficult to synthesize dense bulk polycrystalline bodies (see Non-Patent Document 4).

[0006] A method for adjusting the alkali metal content ratio by substituting alkali metal ions in a glass substrate with protons using corona discharge is known (see Patent Document 1). Also, a method for producing an intercalation material has been proposed in which a first ion source containing first ions that do not form a structural framework and a first object to be processed as a host are stacked or placed opposite each other, and second ions of the same sign as the first ions are implanted into the first ion source from the side opposite the first object to be processed, thereby causing the first ions contained in the first ion source to migrate as guests to the first object to be processed and perform intercalation (see Patent Document 2). For example, the object to be processed is TaS2, the first ion source is a glass substrate, and the first ions are Li + and the second ion is a proton. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-117167 [Patent Document 2] International Publication No. 2017 / 188204 [Non-patent literature]

[0008] [Non-Patent Document 1] Phys. Rev. B 62 R7707(2000) [Non-patent document 2] Phys. Chem. 17 13640(2015) [Non-patent document 3] Nat. Commun. 9 772(2018) [Non-patent document 4] Journal of the Crystallographic Society of Japan, 55 242(2013) [Non-patent document 5] Nat. Mater. 11 507(2012) Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, the problem to be solved by this invention is to provide various ion-extracting compounds using various compounds such as type II group IV clathrate compounds as starting materials, and methods for producing the same.

[0010] Another object of the present invention is to provide an ion-substituted product using various substances such as oxides as starting materials, and a method for producing the same.

[0011] A further object of the present invention is to provide an intercalation compound using various compounds having a van der Waals gap in their structure as starting materials, and a method for producing the same.

[0012] A further object of the present invention is to provide a method for producing an intercalation compound, which can easily produce an intercalation compound containing an alkaline earth metal.

[0013] Still another problem to be solved by this invention is to 14 The present invention provides a pressure cell for high-pressure solid-state electrochemistry that is suitable for use in producing ion-extraction compounds, ion-substitution compounds, intercalation compounds, etc. by electrochemically treating various substances, such as oxides, compounds having van der Waals gaps, as starting materials, under high pressure. [Means for solving the problem]

[0014] In order to solve the above problems, the present invention provides: The ion-extracted compound is a compound in which at least a part of the ion to be extracted has been extracted from the compound to which the ion is most weakly bound.

[0015] Here, the compound with the weakest bond to the ion to be extracted typically has a covalent framework structure. Examples of such compounds include II-type group IV clathrate compounds containing Na ions (e.g., II-type Si clathrate compounds, II-type Si-Ge clathrate compounds, etc.) and NaAlB 14 In this case, the ion is a Na ion. In II-type group IV clathrate compounds, group IV elements are covalently bonded to form a cage structure. For example, in II-type Si clathrate compounds, Si forms a cage structure, and in II-type Si-Ge clathrate compounds, Si and Ge form a cage structure by covalent bonding. NaAlB 14 has the covalent backbone of B.

[0016] A type-II group-IV clathrate compound typically consists of a single crystal large enough to contain a sphere with a radius of at least 200 μm, for example, a single crystal with dimensions of 0.5 mm or more in all directions. As mentioned above, it has been difficult to remove Na ions from a surface of a type-II group-IV clathrate compound single crystal of this size by conventional vacuum annealing methods.

[0017] Type II group IV clathrate compounds can be used, for example, as direct transition semiconductors, thermoelectric conversion materials, electrode materials for various ion batteries, gas storage materials, and the like.

[0018] NaAlB 14 It may be single crystal or polycrystalline.

[0019] The present invention also provides: The method for producing an ion-extracting compound includes a step of contacting a compound in which the ion to be extracted is most weakly bonded with a conductor of the ion, and then performing heat treatment while applying a voltage of such polarity to the compound and the conductor of the ion that the ion of the compound moves to the conductor of the ion, thereby extracting the ion from the compound.

[0020] The magnitude of the applied voltage and the conditions of the heat treatment (temperature, time, atmosphere), etc., can be appropriately selected depending on the compound in which the ion to be extracted is most weakly bound. An example of the compound in which the ion to be extracted is the most weakly bound is a II-type, Group-IV clathrate compound containing a Na ion, where the ion is a Na ion. In this case, the Na ion is extracted from the II-type, Group-IV clathrate compound by applying a voltage to the II-type, Group-IV clathrate compound and the Na ion conductor while the II-type, Group-IV clathrate compound is in contact with the Na ion conductor and then performing heat treatment so that the II-type, Group-IV clathrate compound side has a higher potential.

[0021] The present invention also provides: The method for producing an ion-extracting compound includes a step of contacting a compound in which an ion to be extracted is most weakly bonded with the ion conductor, and then performing heat treatment under high pressure while applying a voltage to the compound and the ion conductor of such polarity that the ion of the compound moves to the ion conductor, thereby extracting the ion from the compound.

[0022] This method for producing ion-extracting compounds is a novel synthesis technique that allows for simultaneous adjustment of three parameters: pressure, temperature, and voltage. By applying high pressure to the compound with the weakest ion bonds and to the ion conductor, a good contact interface between solid phases can be formed on a nanoscale. A constant pressure is constantly applied even against the volume change of the crystal due to ion diffusion, so that a good interface for ion diffusion can be continuously obtained. Here, the magnitude of the applied voltage, the magnitude of pressure, and the heat treatment conditions (temperature, time, atmosphere) can be appropriately selected depending on the compound with the weakest ion bonds to be extracted. An example of the compound with the weakest ion bonds to be extracted is NaAlB 14 and the ions are Na ions. In this case, NaAlB 14 The NaAlB 14 and NaAlB as a Na ion conductor. 14By applying a voltage so that the side has a high potential, the NaAlB 14 Removes Na ions from the

[0023] The present invention also provides: This is an ion-substituted compound in which at least a part of the first ion to be extracted from the compound to which the first ion is most weakly bound is extracted, and a second ion is introduced into the site from which the first ion was extracted.

[0024] Here, the compound in which the first ion to be extracted is most weakly bound is, for example, a sintered oxide, where the first ion is an oxide ion and the second ion is a hydride ion. Such an oxide is typically, but not limited to, a perovskite oxide.

[0025] The present invention also provides: The method for producing an ion-substituted compound includes the steps of sandwiching a compound to which a first ion to be extracted is most weakly bound between a conductor of a second ion to be introduced into the compound and the first ion conductor, and performing heat treatment under high pressure while applying a voltage between the first ion conductor and the second ion conductor, the voltage having a polarity such that the first ion of the compound moves to the first ion conductor and the second ion of the second ion conductor moves to the compound, thereby extracting the first ion from the compound and introducing the second ion into the site of the compound from which the first ion was extracted.

[0026] This ion-exchanger manufacturing method is a novel synthesis technique that allows simultaneous adjustment of three parameters: pressure, temperature, and voltage. By applying high pressure to the second ion conductor, the compound to which the first ion to be extracted is most weakly bound, and the first ion conductor, a favorable solid-phase contact interface can be formed on a nanoscale. Since a constant pressure is constantly applied even against the volume change of the crystal due to ion diffusion, a favorable interface for ion diffusion can be continuously obtained. The magnitude of the applied voltage, the magnitude of the pressure, and the heat treatment conditions (temperature, time, atmosphere) can be appropriately selected depending on the compound to which the first ion to be extracted is most weakly bound. This compound is, for example, a sintered oxide, in which the first ion is an oxide ion and the second ion is a hydride. Such oxides are typically, but not limited to, perovskite oxides. In this case, a hydride conductor, an oxide, and an oxide ion conductor are laminated in this order, and a heat treatment is performed under high pressure while applying a voltage between the hydride conductor and the oxide ion conductor so that the oxide ion conductor side has a higher potential, thereby removing oxide ions from the oxide and introducing hydride into the sites of the oxide from which the oxide ions have been removed. This makes it possible to introduce hydrogen into the sintered oxide, and an oxyhydride can be easily produced.

[0027] The present invention also provides: It is an intercalation compound in which metal ions are introduced into a compound having a van der Waals gap in its structure.

[0028] Here, compounds having a van der Waals gap in their structure, i.e., van der Waals compounds, include, for example, compounds with a layered structure and fibrous materials. In compounds with a layered structure, the van der Waals gap is the space between layers, while in fibrous materials, the van der Waals gap is the space created between one-dimensionally extending fibers. These compounds and fibrous materials with a layered structure include, for example, transition metal dichalcogenides, transition metal trichalcogenides, Group 13 chalcogenides, Group 14 chalcogenides, layered superconducting materials, layered nitrides, and carbon-based materials. Of these, transition metal dichalcogenides in particular are MCh2 (M = Ti, Zr, Hf, V, Nb, Ta, Mo, W, etc., Ch = S, Se, Te), such as TaS2, NbSe2, NbS2, FeSe2, and MoTe2. Transition metal trichalcogenides include MCh3 (M = Ti, Zr, Hf, V, Nb, Ta, Mo, W, etc., Ch = S, Se, Te), such as TaS3, TaSe3, and NbSe3. Group 13 chalcogenides include GaS, GaSe, GaTe, and InSe. Group 14 chalcogenides include GeS, SnS2, SnSe2, and PbO. Layered superconducting materials include copper oxide high-temperature superconductors, iron-based superconductors, and BiCh2-based superconductors (Ch = S, Se, Te), such as Bi2Sr2CaCu2O. x , LnFePnO 1-x F x , FeSe 1-x S x , FeTe 1-x S x , FeTe 1-x Se x , Ln(O 1-x F x)BiCh2 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ch = S, Se, Te, Pn = As, P), for example, La(OF)BiS2, Ce(OF)BiS2, Pr(OF)BiS2, Nd(OF)BiS2, La(OF)BiSe2, La(OF)BiSeS, La(OF)BiS2, etc. Layered nitrides include TiNCl, ZrNCl, HfNCl, etc. Carbon-based materials include graphite, carbon nanotubes, fullerenes, bilayer graphene, etc. Metal ions are not particularly limited, but include, for example, Mg ions, Ag ions, Cu ions, etc.

[0029] The present invention also provides: The method for producing an intercalation compound includes a step of contacting a compound having a van der Waals gap in its structure with a conductor of a metal ion to be introduced into the compound, and then performing heat treatment under high pressure while applying a voltage to the compound and the conductor so that the conductor side has a high potential, thereby introducing the metal ion from the conductor into the compound.

[0030] This method for producing intercalation compounds is a novel synthesis technique that allows for simultaneous adjustment of three parameters: pressure, temperature, and voltage. By applying high pressure to the compound and conductor, a favorable solid-phase contact interface can be formed on the nanoscale. A constant pressure is constantly applied to counter the volumetric changes of the crystals that accompany ion diffusion, ensuring a sustained interface favorable for ion diffusion. The magnitude of the applied voltage, the magnitude of the pressure, and the heat treatment conditions (temperature, time, atmosphere) can be appropriately selected depending on the compound that has a van der Waals gap in its structure and the metal ion to be introduced into the compound.

[0031] The present invention also provides: The method for producing an intercalation compound includes a step of firing a mixed powder consisting of a powder of a compound having a van der Waals gap in its structure and a powder of an alkaline earth metal hydride.

[0032] In this invention of the method for producing an intercalation compound, an intercalation compound containing an alkaline earth metal can be produced by calcining a mixed powder consisting of a powder of a compound having a van der Waals gap in its structure and a powder of an alkaline earth metal hydride. The compound having a van der Waals gap in its structure, i.e., the van der Waals compound, is as described in relation to the above intercalation compound invention. The alkaline earth metal is Mg, Ca, Sr, Ba, etc. The alkaline earth metal hydride is, for example, MgH2, CaH2, SrH2, BaH2, etc. The calcination temperature and calcination time can be appropriately selected depending on the compound having a van der Waals gap in its structure and the alkaline earth metal hydride. Calcination can be carried out at normal pressure or under high pressure.

[0033] The present invention also provides: a tubular sample chamber in which a sample is accommodated; a heater provided so as to surround the sample chamber; a support having a through hole for accommodating the sample chamber and the heater; a first current introduction terminal and a second current introduction terminal provided on a side surface of the support member so as to face each other across the through hole and be electrically connected to the heater; a first lid having a first voltage application terminal and provided in contact with one end of the sample chamber so as to close one end of the through-hole of the support, and a second lid having a second voltage application terminal and provided in contact with the other end of the sample chamber so as to close the other end of the through-hole; A pressure cell for high-pressure solid-state electrochemistry having:

[0034] Here, a high-pressure solid-state electrochemical pressure cell refers to a pressure cell used to perform electrochemical processing on a solid target compound (sample) under high pressure. The size and shape of the sample chamber can be selected appropriately depending on the size and shape of the sample, and is, for example, cylindrical. The shape of the support is selected as needed and is not particularly limited, and may be, for example, a square prism or a regular octahedron. Pressure is typically applied to this high-pressure solid-state electrochemical pressure cell by pressing it from the outside with a high-pressure anvil. [Effects of the Invention]

[0035] According to this invention, various ion-extracted compounds such as type II group IV clathrate compounds from which Na ions have been extracted, various ion-substituted compounds such as oxides in which oxide ions have been replaced with hydrides, and various intercalation compounds such as TaS2 containing Mg ions and MoTe2 containing Ag ions can be easily obtained. [Brief explanation of the drawings]

[0036] [Figure 1A] FIG. 1 is a schematic diagram showing a II-type group-IV clathrate compound as a starting material for a Na-ion-extracted II-type group-IV clathrate compound according to a first embodiment of the present invention. [Figure 1B] 1B is a schematic diagram showing a dodecahedron made up of 20 group IV elements that constitute the type II group IV clathrate compound shown in FIG. 1A. FIG. [Figure 1C] 1B is a schematic diagram showing a hexahedron made up of 28 group IV elements that constitute the type II group IV clathrate compound shown in FIG. 1A. FIG. [Figure 2A] 1 is a schematic diagram showing a method for producing a Na ion-extracted II-type group-IV clathrate compound according to a first embodiment of the present invention. [Figure 2B] 1 is a schematic diagram showing a method for producing a Na ion-extracted II-type group-IV clathrate compound according to a first embodiment of the present invention. [Figure 3A]FIG. 1 is a schematic diagram showing Na24Si136, an example of a II-type group-IV clathrate compound. [Figure 3B] 3B is a schematic diagram showing Si136 obtained by removing Na ions from Na24Si136 shown in FIG. 3A. FIG. [Figure 4A] 1 is a photograph, substituted for a drawing, showing a solid-state electrochemical device used in carrying out a method for producing a Na ion-extracted II-type Si clathrate compound according to Example 1. [Figure 4B] 4B is a photograph substituting for a drawing showing an enlarged view of the periphery of the sample of the solid-state electrochemical device shown in FIG. 4A. [Figure 5] 1 is a photograph, substituted for a drawing, showing a Na ion-extracted single crystal Na24-xSi136 produced by carrying out the production method of a Na ion-extracted type II Si clathrate compound according to Example 1. [Figure 6] FIG. 6 is a schematic diagram showing the analysis positions of the Na-ion-extracted single crystal Na24-xSi136 shown in FIG. 5. [Figure 7A] 7 is a photograph, shown in place of a drawing, illustrating a cross section of the Na-ion-extracted single crystal Na24-xSi136 shown in FIG. 6 taken along analysis line 1. [Figure 7B] 7B is a photograph showing the Na distribution in the cut surface of the Na ion-extracted single crystal Na24-xSi136 shown in FIG. 7A. [Figure 8A] 7 is a photograph, shown in place of a drawing, illustrating a cross section of the Na-ion-extracted single crystal Na24-xSi136 shown in FIG. 6 taken along analysis line 2. [Figure 8B] 8B is a photograph showing the Na distribution in a cut surface of the Na ion-extracted single crystal Na24-xSi136 shown in FIG. 8A. [Figure 9A] 7 is a photograph, shown in place of a drawing, illustrating a cross section of the Na-ion-extracted single crystal Na24-xSi136 shown in FIG. 6 taken along the analysis line 3. [Figure 9B] 9B is a photograph showing the Na distribution in the cut surface of the Na ion-extracted single crystal Na24-xSi136 shown in FIG. 9A. [Figure 10A] 7 is a photograph, shown in place of a drawing, illustrating a cross section of the Na-ion-extracted single crystal Na24-xSi136 shown in FIG. 6 taken along the analysis line 4. [Figure 10B] 10B is a photograph showing the Na distribution in a cut surface of the Na ion-extracted single crystal Na24-xSi136 shown in FIG. 10A. [Figure 11A] 7 is a photograph, shown in place of a drawing, illustrating a cross section of the Na-ion-extracted single crystal Na24-xSi136 shown in FIG. 6 taken along an analysis line 5. [Figure 11B] 11B is a photograph showing the Na distribution in a cut surface of the Na ion-extracted single crystal Na24-xSi136 shown in FIG. 11A. [Figure 12A] 7 is a photograph, shown in place of a drawing, illustrating a cross section of the Na-ion-extracted single crystal Na24-xSi136 shown in FIG. 6 taken along analysis line 6. [Figure 12B] 12B is a photograph showing the Na distribution in the cut surface of the Na ion-extracted single crystal Na24-xSi136 shown in FIG. 12A. [Figure 13A] 7 is a photograph, shown in place of a drawing, illustrating a cross section of the Na-ion-extracted single crystal Na24-xSi136 shown in FIG. 6 taken along an analysis line 7. [Figure 13B] 13B is a photograph showing the Na distribution in a cut surface of the Na ion-extracted single crystal Na24-xSi136 shown in FIG. 13A. [Figure 14A] 7 is a photograph, shown in place of a drawing, illustrating a cross section of the Na-ion-extracted single crystal Na24-xSi136 shown in FIG. 6 taken along an analysis line 8. [Figure 14B] 14B is a photograph showing the Na distribution in the cut surface of the Na ion-extracted single crystal Na24-xSi136 shown in FIG. 14A. [Figure 15] FIG. 7 is a schematic diagram in which the amount of Na in Na24-xSi136 is plotted against the positions of analysis lines 1 to 8 of the Na ion-extracted single crystal Na24-xSi136 shown in FIG. [Figure 16A] FIG. 1 is a schematic diagram showing the measurement results of the X-ray diffraction pattern of single crystal Na24Si136 used as a starting material. [Figure 16B] FIG. 6 is a schematic diagram showing the measurement results of the X-ray diffraction pattern of the Na-ion-extracted single crystal Na24-xSi136 shown in FIG. 5. [Figure 16C]16B. FIG. 16C is a schematic diagram showing an enlarged view of a part of the X-ray diffraction pattern shown in FIG. 16A and a part of the X-ray diffraction pattern shown in FIG. 16B superimposed on each other. [Figure 17] 6 is a schematic diagram showing the measurement results of the electronic conduction characteristics of the single crystal Na24Si136 used as a starting material and the Na ion-extracted single crystal Na24-xSi136 shown in FIG. 5. [Figure 18A] 1 is a photograph showing a comparative example of single crystal Na24Si136. [Figure 18B] 18B is a photograph showing the Na distribution in the single crystal Na24Si136 shown in FIG. 18A. [Figure 19A] 10 is a photograph showing the state of a comparative example of single crystal Na24Si136 after vacuum annealing for three days. [Figure 19B] 19B is a photograph showing the Na distribution in the single crystal Na24Si136 shown in FIG. 19A. [Figure 20A] 10 is a photograph showing the state of a comparative example of single crystal Na24Si136 after annealing in vacuum for eight days. [Figure 20B] 20B is a photograph showing the Na distribution in the single crystal Na24Si136 shown in FIG. 20A. [Figure 21] 10 is a photograph showing the appearance of a comparative example of single crystal Na24Si136 after annealing in vacuum for eight days. [Figure 22] FIG. 1 is a schematic diagram showing the structure of NaAlB14. [Figure 23A] FIG. 10 is a schematic diagram showing a method for producing Na-ion-extracted NaAlB14 according to a second embodiment of the present invention. [Figure 23B] FIG. 10 is a schematic diagram showing a method for producing Na-ion-extracted NaAlB14 according to a second embodiment of the present invention. [Figure 24] 10 is a schematic diagram showing a high-pressure solid-state electrochemical device used to carry out a method for producing Na-ion-extracted NaAlB14 according to Example 2. FIG. [Figure 25] 10 is a photograph, substituted for a drawing, showing a pellet obtained by molding powdered NaAlB14 into a disk shape, which is used as a starting material when carrying out the manufacturing method of Na ion-extracted NaAlB14 according to Example 2. [Figure 26] 10 is a schematic diagram showing the state inside the sample chamber of the high-pressure solid-state electrochemical device after carrying out the method for producing NaAlB14 from which Na ions have been extracted according to Example 2. FIG. [Figure 27A] 10 is a photograph, substituted for a drawing, showing the state inside the sample chamber of the high-pressure solid-state electrochemical device after carrying out the method for producing NaAlB14 from which Na ions have been extracted according to Example 2. [Figure 27B] 27B is a photograph showing an enlarged view of the area enclosed by the square in the upper left corner of FIG. 27A. [Figure 27C] 27B is a photograph substituting for a drawing, showing an enlarged view of the area enclosed by a square in the lower center of FIG. 27A. [Figure 28] 10 is a photograph, substituted for a drawing, showing Na-ion-extracted bulk polycrystalline NaAlB14 produced by carrying out the method for producing Na-ion-extracted NaAlB14 according to Example 2. [Figure 29] 1 is a schematic diagram showing the measurement results of X-ray diffraction patterns of bulk polycrystalline NaAlB14 before Na ion extraction and Na0.06AlB14 after Na ion extraction. [Figure 30] 1 is a schematic diagram showing the measurement results of the electronic conduction characteristics of bulk polycrystalline NaAlB14 before Na ion extraction and Na0.06AlB14 after Na ion extraction. [Figure 31] 10 is a photograph, substituted for a drawing, showing the results of an attempt to produce NaAlB14 electrochemically at normal pressure using a solid-state electrochemical device for comparison with Example 2. [Figure 32] 10 is a schematic diagram showing the results of measuring the change over time in the current flowing through the sample in Example 2 and in the case where solid-state electrochemical treatment was carried out under conditions of normal pressure and 50V. FIG. [Figure 33A] FIG. 4 is a schematic diagram showing a method for producing an oxyhydride according to a third embodiment of the present invention. [Figure 33B] FIG. 4 is a schematic diagram showing a method for producing an oxyhydride according to a third embodiment of the present invention. [Figure 34A] FIG. 10 is a schematic diagram for explaining the mechanism of the method for producing an oxyhydride according to the third embodiment of the present invention. [Figure 34B]FIG. 10 is a schematic diagram for explaining the mechanism of the method for producing an oxyhydride according to the third embodiment of the present invention. [Figure 34C] FIG. 10 is a schematic diagram for explaining the mechanism of the method for producing an oxyhydride according to the third embodiment of the present invention. [Figure 34D] FIG. 10 is a schematic diagram for explaining the mechanism of the method for producing an oxyhydride according to the third embodiment of the present invention. [Figure 35A] 1 is a photograph showing polycrystalline BaTiO3 as a starting material when carrying out a method for producing a BaTiO3-based oxyhydride according to Example 3. [Figure 35B] 10 is a photograph showing BaTiO2.8 H0.2 obtained after carrying out the BaTiO3 manufacturing method according to Example 3. [Figure 36] 35C is a schematic diagram showing measurement results of hydrogen release during temperature rise and fall of BaTiO2.8 H0.2 shown in FIG. 35B. [Figure 37] 35C is a schematic diagram showing the measurement results of the electronic conduction characteristics of BaTiO2.8H0.2 and BaTiO2.94H0.06 shown in FIG. 35B. FIG. [Figure 38A] FIG. 10 is a schematic diagram showing a method for producing an intercalation compound according to a fourth embodiment of the present invention. [Figure 38B] FIG. 10 is a schematic diagram showing a method for producing an intercalation compound according to a fourth embodiment of the present invention. [Figure 39A] 10 is a schematic diagram showing the structure of TaS2 as a starting material when carrying out a method for producing Mg-containing TaS2 according to Example 4. FIG. [Figure 39B] 10 is a schematic diagram showing the structure of Mg-containing TaS2 produced by the method for producing Mg-containing TaS2 according to Example 4. FIG. [Figure 40] 10 is a photograph showing Mg-containing TaS2 produced under the condition of voltage application in the method for producing Mg-containing TaS2 according to Example 4. [Figure 41]10 is a photograph showing Mg-containing TaS2 produced under the condition of no voltage application in the method for producing Mg-containing TaS2 according to Example 4. [Figure 42A] 10 is a photograph showing Ag-containing MoTe2 produced by the method for producing Ag-containing MoTe2 according to Example 5. [Figure 42B] 10 is a photograph substituting for a drawing showing the results of analysis of Ag in Ag-containing MoTe2 produced by the method for producing Ag-containing MoTe2 according to Example 5. [Figure 43A] 10 is a photograph showing Cu-containing MoTe2 produced by the Cu-containing MoTe2 production method according to Example 6. [Figure 43B] 10 is a photograph substituting for a drawing showing the results of analysis of Cu in Cu-containing MoTe2 produced by the method for producing Cu-containing MoTe2 according to Example 6. [Figure 44] 42B is a schematic diagram showing the measurement results of the electronic conduction characteristics of Ag-containing MoTe2 shown in FIG. 42A and Cu-containing MoTe2 shown in FIG. 43A together with the measurement results of the electronic conduction characteristics of MoTe2 before introduction of metal ions. [Figure 45] 10 is a schematic diagram showing the measurement results of the X-ray diffraction pattern of Mg-containing TaS2 produced by the production method of Mg-containing TaS2 according to Example 7. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0037] Hereinafter, modes for carrying out the invention (hereinafter referred to as "embodiments") will be described with reference to the drawings.

[0038] First Embodiment [Sodium ion-extracted type II group IV clathrate compounds] In the Na-ion-extracted type-II group-IV clathrate compound according to the first embodiment, at least some of the Na ions in the type-II group-IV clathrate compound in which the Na ions to be extracted are most weakly bound are extracted, and all of the Na ions may be extracted. In this type-II group-IV clathrate compound, Na ions are encapsulated in a cage structure formed by group IV elements such as Si and Ge.

[0039] [Method of manufacturing type II group IV clathrate compounds with sodium ions removed] Figure 1A shows the structure of a type II group IV clathrate compound in which Na ions (not shown) are most weakly bound. This type II group IV clathrate compound is composed of a dodecahedron consisting of 20 group IV elements, as shown in Figure 1B, and a hexahedron consisting of 28 group IV elements, as shown in Figure 1C. A single-crystal Na-ion-containing type II group IV clathrate compound is typically used as the starting material.

[0040] As shown in FIG. 2A, first, a Na-ion conductor 20 is brought into contact with a type-II, group-IV clathrate compound 10 containing Na ions 11. The Na-ion conductor 20 is a solid electrolyte through which Na ions can diffuse. Next, as shown in FIG. 2B, a heat treatment is performed while applying a voltage of such polarity to the type-II, group-IV clathrate compound 10 and the Na-ion conductor 20 that the Na ions 11 in the type-II, group-IV clathrate compound 10 migrate to the Na-ion conductor 20. Specifically, a voltage V is applied such that the potential of the type-II, group-IV clathrate compound 10 is higher than that of the Na-ion conductor 20. This causes the Na ions 11 to migrate from the type-II, group-IV clathrate compound 10 to the Na-ion conductor 20 and be extracted. The heat treatment temperature is, for example, 350°C to 600°C, typically 400°C to 500°C. The heat treatment time is appropriately selected taking into consideration the size of the II-type group-IV clathrate compound 10, the heat treatment temperature, and the like. Generally, the larger the size of the II-type group-IV clathrate compound 10, the longer the heat treatment time must be; for example, from 10 hours to 1 month, and typically from 1 day to 10 days. The heat treatment atmosphere is preferably, for example, an inert gas atmosphere such as nitrogen (N) or argon (Ar), or a vacuum atmosphere. In this manner, Na ions 11 are removed from the II-type group-IV clathrate compound 10, thereby producing a Na ion-extracted II-type group-IV clathrate compound 30.

[0041] FIG. 3A shows an example of a type II group IV clathrate compound 10, Na 24 Si 136 Also, Figure 3B shows this Na 24 Si 136 All Na ions are removed from Si 136 Shows.

[0042] Example 1 In Example 1, polygonal single crystal Na was used as the starting material. 24 Si 136The sodium ion conductor 20 used was a cylindrical Na3Zr2Si2PO4 with a diameter of approximately 4.2 mm, which is a type of solid electrolyte having a NASICON (sodium (Na) Super Ionic Conductor) type structure. 12 Figures 4A and 4B show the solid-state electrochemical device used in the experiment, and Figure 4B is an enlarged view of the area enclosed by the dashed line in Figure 4A. As shown in Figures 4A and 4B, Na3Zr2Si2PO 12 and single crystal Na 24 Si 136 A stainless steel (SUS) anode electrode is lowered from above to form a single crystal Na 24 Si 36 A positive voltage of 50 V was applied to the anode electrode relative to the cathode electrode, and heat treatment was carried out for 8 days in a nitrogen atmosphere at 450°C. When a positive voltage was applied to the anode electrode relative to the cathode electrode, Na3Zr2Si2PO 12 causes DC polarization, and this Na3Zr2Si2PO 12 Single crystal Na 24 Si 136 The Na ion concentration near the contact surface with the single crystal Na decreases. 24 Si 136 and Na3Zr2Si2PO 12 A large difference in Na ion concentration (chemical potential difference) is formed between the two, resulting in the formation of a single crystal of Na 24 Si 136 The Na ions in Na3Zr2Si2PO 12 In this way, single crystal Na 24 Si 136 Na ions were removed from

[0043] As described above, single crystal Na 24 Si 136 Single crystal Na with Na ions removed 24-x Si 136 The photographs taken are shown in Figure 5. From Figure 5, it is clear that the single crystal Na 24-x Si 136 It can be seen that there is no contamination on the surface of the single crystal Na due to the precipitation of impurities resulting from the volatilization of Na. 24-xSi 136 As shown in Figure 6, this single crystal Na 24-x Si 136 Photographs of cross sections cut along analysis lines 1 to 8 (shown by dashed lines) at different heights in the vertical direction in the direction of the applied voltage (direction of the electric field E) were taken, and Na was analyzed by fluorescent X-ray analysis. Photographs of the cut sections at the positions of analysis lines 1 to 8 are shown in Figures 7A, 8A, 9A, 10A, 11A, 12A, 13A, and 14A, respectively. The distributions of Na in the cut sections at the positions of analysis lines 1 to 8 are shown in Figures 7B, 8B, 9B, 10B, 11B, 12B, 13B, and 14B, respectively. Figures 7B, 8B, 9B, 10B, 11B, 12B, 13B, and 14B are the distributions of Na in the single crystal Na shown in Figures 7A, 8A, 9A, 10A, 11A, 12A, 13A, and 14A, respectively. 24 Si 136 15 shows the results of the analysis of Na by X-ray fluorescence analysis (color mapping image converted to monochrome; the same applies below). Figure 15 shows the results of the analysis of Na by X-ray fluorescence analysis (color mapping image converted to monochrome; the same applies below). 24-X Si 136 The Na content was determined from the Na Kα ray intensity and Si Kα ray intensity in fluorescent X-ray analysis. The scale of the horizontal axis in Fig. 15 is the same as that of the single crystal Na shown in Fig. 6. 24-X Si 136 The distance measured downward from the top surface of the single crystal Na before the Na ions were extracted is shown in Fig. 15. 24 Si 136 The amount of Na in the single crystal is shown by the dotted line. 24-X Si 136 The amount of Na was about 2.5 at any position on analysis lines 1 to 8, and it was confirmed that Na was removed uniformly throughout the crystal.

[0044] FIG. 16A shows the single crystal NaCl used as the starting material before Na ions were removed. 24 Si 136 16B shows the results of measuring the X-ray diffraction pattern of the single crystal Na ion-extracted shown in FIG. 24-X Si 13616A and 16B show the results of measuring the X-ray diffraction pattern of the single crystal Na after Na ions were extracted. Figure 16C shows the area around the 555 diffraction peak of the X-ray diffraction pattern shown in Figure 16A and the area around the 555 diffraction peak of the X-ray diffraction pattern shown in Figure 16B, superimposed on each other. 24-X Si 136 The X-ray diffraction peak of the parent phase is Na 24 Si 136 The X-ray diffraction peaks were almost unchanged from those of the single crystal Na ions extracted, confirming that the clathrate structure was maintained. 24-X Si 136 The X-ray diffraction peak of is shifted to the higher angle side, which is consistent with the decrease in lattice constant due to the removal of Na ions.

[0045] Single crystal sodium 24 Si 136 and single crystal Na with Na ions removed 24-X Si 136 The electron conduction characteristics of the single crystal Na ions were measured. The measurement results are shown in Figure 17. The vertical axis of Figure 17 represents resistivity (mΩcm) and the horizontal axis represents absolute temperature. As shown in Figure 17, the electron conduction characteristics change to a semiconducting type as Na ions are removed. 24-X Si 136 is single crystal Na 24 Si 136 In contrast, the electron conduction characteristics are 10 4 times, and 10 times at low temperatures 7 It was confirmed that the electron conductivity increased by 2 times. 24-X Si 136 was able to obtain.

[0046] As a comparative example, the results of removing Na ions by the conventional vacuum annealing method will be explained. Figures 18A and 18B show the results of the untreated single crystal Na used in this experiment. 24 Si 136 19A and 19B show the single crystal Na after 3 days of vacuum annealing. 24 Si 13620A and 20B show the single crystal Na after 8 days of vacuum annealing. 24 Si 136 The photographs of the single crystal Na after 8 days of vacuum annealing are shown in Fig. 21. 24 Si 136 These photographs show that even after long-term vacuum annealing, the single crystal Na 24 Si 136 It can be seen that the area where Na ions can be removed is limited to about 200 μm from the surface, and the amount of Na in the entire crystal remains almost unchanged. Furthermore, as a result of this treatment, impurities resulting from the volatilization of Na are precipitated on the surface of the single crystal sample, contaminating the surface, as shown in Figure 21.

[0047] As described above, according to the first embodiment, unlike conventional methods for extracting Na ions using vacuum annealing, Na ions can be extracted uniformly and easily from the II-type, group-IV clathrate compound 10 even for large crystals with dimensions exceeding 0.4 mm, typically 1 mm, in all directions. This makes it possible to easily produce the Na-ion-extracted II-type, group-IV clathrate compound 30 from which a desired amount of Na ions has been extracted. Furthermore, unlike vacuum annealing, the surface of the Na-ion-extracted II-type, group-IV clathrate compound 30 is not contaminated by the deposition of impurities resulting from the volatilization of Na. This Na-ion-extracted II-type, group-IV clathrate compound 30 is not only suitable as a direct transition semiconductor for use as a photoelectric conversion material for solar power generation, but also as a thermoelectric conversion material, an electrode material for various ion batteries such as Li-ion batteries that utilize the voids remaining after the extraction of Na ions, and an occlusion material for hydrogen gas, etc.

[0048] Second Embodiment [Ion extraction NaAlB 14 ] Ion extraction NaAlB according to the second embodiment 14 In the case of NaAlB, the Na ion to be extracted is the weakest bond. 14At least some of the Na ions may be removed, and all of the Na ions may be removed. 14 The NaAlB 14 The structure of

[0049] [Ion extraction NaAlB 14 Manufacturing method] As shown in FIG. 23A, first, NaAlB 14 The Na ion conductor 60 is brought into contact with the crystal 50. The Na ion conductor 60 is a solid electrolyte in which Na ions can diffuse, similar to the Na ion conductor 20. Next, as shown in FIG. 23B, these NaAlB 14 Crystal 50 and Na ion conductor 60 NaAlB 14 A voltage of such polarity that the Na ions 51 of the crystal 50 move to the Na ion conductor 60 is applied. Specifically, the voltage is applied from the Na ion conductor 60 to NaAlB 14 By applying a voltage V such that the potential of the crystal 50 is higher, the NaAlB 14 The Na ions 51 are moved from the crystal 50 to the Na ion conductor 60 and then extracted. The temperature of this heat treatment is, for example, 300°C or higher and 1000°C or lower, typically 450°C or higher and 800°C or lower. The time of the heat treatment is 14 It is selected appropriately taking into consideration the size of the crystal 50 and the temperature of the heat treatment, and is generally NaAlB 14 The larger the size of the crystal 50, the longer the heating time must be, for example, 5 hours to 10 days, typically 10 hours to 2 days. The pressure during the heat treatment is, for example, 0.5 GPa to 10 GPa. The heat treatment atmosphere is preferably an inert gas atmosphere such as N2 or Ar. In this way, NaAlB 14 By removing Na ions 51 from the crystal 50, Na ion extraction NaAlB 14 A crystal 70 can be produced.

[0050] Figure 24 shows the ion extraction of NaAlB 141 shows a high-pressure solid-state electrochemical device used to carry out the manufacturing method of 1. The high-pressure solid-state electrochemical device has a pressure cell for high-pressure solid-state electrochemistry. As shown in Figure 24, this high-pressure solid-state electrochemical pressure cell has a tubular, for example cylindrical, sample chamber 110 in which a sample is housed, a heater 120 arranged to surround the sample chamber 110, a square prism-shaped, typically cubic, support 130 having a through-hole 131 in which the sample chamber 110 and heater 120 are housed, a first current introduction terminal 140 and a second current introduction terminal 150 arranged on the side of the support 130 and electrically connected to the heater 120 so as to face each other across the through-hole 131, a first lid 160 having a first voltage application terminal 161 arranged in contact with the upper end of the sample chamber 110 so as to cover the upper end of the through-hole 131 in the support 130, and a second lid 170 having a second voltage application terminal 171 arranged in contact with the lower end of the sample chamber 110 so as to cover the lower end of the through-hole 131. The heater 120 is sandwiched between rings 111 and 112 fitted to the outer periphery of the sample chamber 110. The sample chamber 110 is made of a heat-resistant material such as ceramics. The heater 120 is, for example, a carbon heater. The support 130 is made of a heat-resistant material such as pyroferrite. The first current introduction terminal 140 and the second current introduction terminal 150 are provided through through-holes 131 and 132 on a pair of opposing side surfaces of the support 130, and their respective tips are in contact with the heater 120. The first current introduction terminal 140 and the second current introduction terminal 150 are made of, for example, Cu electrodes. The first lid 160 and the second lid 170 have the same shape and size as the cross-sectional shape of the support 130. The first voltage application terminal 161 is provided on the back side of the first lid 160, i.e., at the center of the side facing the interior of the support 130. Similarly, second voltage application terminal 171 is provided on the front side of second lid 170, that is, on the side facing the inside of support 130, for example, at the center. First lid 160 and second lid 170, including first voltage application terminal 161 and second voltage application terminal 171, are formed of, for example, Mo electrodes. First current introduction terminal 140 and second current introduction terminal 150 are connected to temperature control circuit 180 provided externally.The first voltage application terminal 161 and the second voltage application terminal 171 are connected to an externally provided voltage application circuit 190. Pressure is applied to this high-pressure solid-state electrochemical pressure cell from six directions by pressing the six surfaces of the support 130 with high-pressure anvils (only the top, bottom, left, and right high-pressure anvils 201 to 204 are shown in Figure 27).

[0051] Example 2 A pressure cell for high-pressure solid-state electrochemistry was fabricated. The sample chamber 110 was formed from a BN cylinder with an inner diameter of 4.4 mm, an outer diameter of 5.5 mm, and a height of 9 mm. The heater 120 was formed from a carbon heater with a thickness of 0.5 mm and a height of 7 mm, and the rings 111 and 112 were made of BN. The support 130 was a square prism made of pyroferrite with a side length of 12.5 mm, a height of 12.5 mm, and a central through-hole with a diameter of 6.5 mm. The first current introduction terminal 140 and the second current introduction terminal 150 were formed from cylindrical Cu electrodes with a diameter of 2.0 mm and a length of 3.0 mm. The first lid 160 and the second lid 170 were each made from Mo electrodes.

[0052] As shown in Figure 25, NaAlB 14 The powder was formed into a disk-shaped pellet, which was then sintered to produce a disk-shaped bulk polycrystalline body with a diameter of 4.3 mm and a thickness of 2.0 mm. As shown in Figure 26, a carbon electrode was placed inside the sample chamber 110, and zeolite was filled on top of it as a Na ion conductor 60. On top of that, a bulk polycrystalline body of NaAlB 14 The substrate 130 was placed on the support 130, and the first lid 160 was closed. Then, a voltage V was applied to the first voltage application terminal 161 and the second voltage application terminal 171 by a high-voltage solid-state electrochemical power supply, and a current was passed between the first current introduction terminal 140 and the second current introduction terminal 150 by a heating power supply, and heating was performed by a carbon heater. At the same time, a high pressure was applied by pressing each of the six surfaces of the support 130 with a high-pressure anvil. The voltage V was 50 V, the heating temperature was 550°C, and the pressure was 1 GPa. As a result, as shown in FIG. 27A, a bulk polycrystalline NaAlB 14 As a result, as shown in Figure 28, the black Na ions were transferred to the zeolite and were extracted.x AlB 14 (x=0.06), that is, Na 0.06 AlB 14 Figure 27B shows an enlarged photograph of the area enclosed by the square in the upper left of Figure 27A. Figure 27C shows an enlarged photograph of the area enclosed by the square in the lower center of Figure 27A. As shown in Figure 27C, NaAlB 14 It can be seen that the Na ions extracted from the NaAlB migrate through the zeolite and accumulate in the lower layer. 14 and Na ions removed x AlB 14 The results of powder X-ray diffraction measurements using synchrotron radiation (Spring 8) are shown in Figure 29. For comparison, Figure 29 also shows the AlB 14 As shown in Figure 29, the X-ray diffraction pattern of NaAlB 14 and Na ions removed 0.06 AlB 14 It can be seen that the X-ray diffraction pattern of the Na ion-removed Na ion is in good agreement with the X-ray diffraction pattern obtained by simulation. 0.06 AlB 14 is the matrix (AlB 14 It was confirmed that the structure of NaAlB 14 and Na 0.06 AlB 14 The electron conduction characteristics of Na were measured. The results are shown in Figure 30. 0.06 AlB 14 is NaAlB 14 The electron conduction characteristics are 10 4 This is because the 14 This is thought to be due to hole doping caused by the removal of Na ions from the crystal grains, and a reduction in intergranular resistance caused by the densification of the crystal grains.

[0053] For comparison, in the manufacturing method shown in FIGS. 23A and 23B, the NaAlB2O3 obtained by applying 50 V at normal pressure without applying high pressure and performing solid-state electrochemical treatment was 14The sample is shown in Figure 31. As shown in Figure 31, NaAlB 14 It can be seen that the sample is fractured and island-like. In other words, because high pressure is not applied at normal pressure, a dense contact interface is not obtained, and as will be explained below, an increase in current due to the diffusion of Na ions is not observed. Figure 32 shows the results of measurements of the change over time in the current flowing between the first voltage application terminal 161 and the second voltage application terminal 171, and therefore the current flowing through the sample, when high-pressure solid-state electrochemical processing was performed under conditions of 1 GPa and 50 V in Example 2 and when solid-state electrochemical processing was performed under conditions of normal pressure and 50 V. As shown in Figure 32, current flows in Example 2, but no current flows when solid-state electrochemical processing is performed under conditions of normal pressure and 50 V. In other words, without the application of high pressure, Na ions do not diffuse and no current flows.

[0054] According to the second embodiment, NaAlB is produced by high-pressure solid-state electrochemical method using voltage application, high-temperature heating, and high-pressure application. 14 The Na ions 51 can be extracted from the crystal 50, and the Na ion-extracted NaAlB 14 The crystal 70 can be easily produced. 14 Crystal 70 is a compound that is extremely difficult to synthesize by conventional solid-state reaction methods. 14 By introducing hydrogen into the strong covalently bonded framework structure formed by B, the crystal 70 is being considered for use as a hydrogen storage material or proton conductor with high cycle characteristics.

[0055] Third Embodiment [Acid hydride] In the oxyhydride according to the third embodiment, the oxide ions (O 2- ) is the weakest bond, and at least some of the oxide ions in the sintered oxide are hydrides (H - The oxide is, for example, a perovskite oxide represented by ABO3, such as BaTiO3 or SrTiO3, but is not limited thereto.

[0056] [Method for producing acid hydrides] As shown in FIG. 33A, first, H is applied to the top and bottom of the sintered oxide 310. - Conductors 320 and O 2- Next, as shown in FIG. 33B, in this state, H - Conductors 320 and O 2- O between the oxide 310 and the conductor 330 2- 311 is O 2- Move to conductor 330 and H - Conductor 320 H - A voltage of polarity such that 321 moves to oxide 310, specifically H - Conductor 320 to O 2- By applying a voltage V such that the potential of the conductor 330 is higher, heat treatment is performed under high pressure, and O from the oxide 310 is generated. 2- Removal of 311 and H - H from conductor 320 to oxide 310 - 321 is simultaneously implanted. 2- 311 to H - By replacing the oxide 310 with 321, an oxyhydride 340 can be produced. The temperature of this heat treatment is, for example, 300°C to 1000°C, typically 400°C to 700°C. The heat treatment time is appropriately selected taking into account the size of the oxide 310 and the heat treatment temperature. Generally, the larger the size of the oxide 310, the longer the heat treatment time is required. For example, the heat treatment time is 5 hours to 10 days, typically 10 hours to 3 days. The pressure during the heat treatment is, for example, 0.5 GPa to 10 GPa. This oxyhydride production method can easily produce the oxyhydride 340, which is a thermodynamically metastable substance that cannot be obtained by a typical solid-state reaction. In particular, by applying a high pressure of, for example, several GPa, the hydrogen solid solubility in the oxide 310 can be rapidly increased. Under such high pressure, H - Conductor 320 to H -This allows the metal to be electrochemically diffused between solids without being vaporized as hydrogen gas, smoothly promoting the hydrogenation reaction of the oxide 310. Such a material synthesis technology that combines high-pressure application and electrochemistry has not been reported to date.

[0057] Here, the O to be removed 2- is the weakest bonded oxide, O 2- H - The mechanism of substitution will be explained using BaTiO3 as an example. Figure 34A shows the potential of each atom that constitutes BaTiO3. E in Figure 34A represents energy. From Figure 34A, the potential of Ti is the deepest, the potential of Ba is the next deepest, while O 2- The shallowest and therefore weakest bond is shown in Figure 34B. 2- O 2- The state after removal is shown in Figure 34C. 2- After the removal of H, the site becomes a stable site for an anion. Therefore, as shown in Figure 34D, H - As a result, O in BaTiO3 can be introduced. 2- H - can be replaced by

[0058] Example 3 In Example 3, a sintered white BaTiO3 polycrystalline body having a diameter of 4.3 mm and a thickness of 1.2 mm was used as the oxide 310. The BaTiO3 polycrystalline body was sintered at 1200°C. This BaTiO3 polycrystalline body is shown in Figure 35A. - The conductor 320 was made of MgH2 with a diameter of 4.2 mm and a thickness of 2 mm. 2-Conductor 330 was made of yttria (Y2O3) stabilized zirconia (ZrO2) (YSZ) (yttria content was 10%) with a diameter of 4.2 mm and a thickness of 1.5 mm. In a sample chamber of a high-pressure solid-state electrochemical cell similar to that of Example 2, a pellet of mixed powder of Ti and YSZ with a diameter of 4.2 mm and a thickness of 2.3 mm was placed in the bottom layer, and a YSZ (10%) layer, BaTiO3 polycrystalline body, and MgH2 were layered on top of that in that order. A carbon electrode was placed in the top layer, and first lid 160 was closed. Then, while applying 50 V to the first voltage application terminal 161 and the second voltage application terminal 171 from a high-voltage solid-state electrochemical power supply, a current was passed between the first current introduction terminal 140 and the second current introduction terminal 150 from a heating power supply, and the support 130 was heated to 550°C using a carbon heater, and a high pressure of 1 GPa was applied by pressing the six surfaces of the support 130 with high-pressure anvils 201 to 204. In other words, voltage application, high-temperature heating, and high pressure application were performed simultaneously. As a result, O was removed from the BaTiO3 polycrystal. 2- moves to the YSZ (10%) layer, and O 2- At the same time as the removal of 2- The BaTiO3 polycrystal from which the ions were removed was then filled with H from MgH2. - As a result, as shown in FIG. 35B, O 2- H - A dense, bluish-black polycrystalline body was obtained as an oxyhydride substituted with BaTiO. Figure 36 shows the results of mass analysis of the polycrystalline body thus obtained, which was heated in a nitrogen atmosphere. From Figure 36, H2 release was clearly observed from around 400°C, and it was confirmed that hydrogen had been introduced up to about x = 0.2. In other words, the polycrystalline body obtained was BaTiO 2.8 H 0.2 It was possible to identify it.

[0059] FIG. 37 shows the BaTiO 2.8 H 0.2 Polycrystalline and similarly obtained BaTiO 2.94 H 0.06The results of measuring the electronic conductivity of the polycrystalline material are shown in Figure 37. For comparison, the results of measuring the electronic conductivity of BaTiO produced by a conventional method reported in Non-Patent Document 5 are shown in Figure 37. 2.7 H 0.3 The electron conduction characteristics of the polycrystalline BaTiO 2.8 H 0.2 The polycrystalline material is BaTiO reported in Non-Patent Document 5. 2.7 H 0.3 The electron conduction characteristics are 10 5 The resistivity ρ was improved by more than 10 -5 This is because BaTiO 2.8 H 0.2 It is believed that the polycrystalline body is a sintered body, which results in a dense sample, and this is due to the reduction in intergranular resistance.

[0060] According to the third embodiment, O is converted from oxide 310 by high-pressure solid-state electrochemical method using voltage application, high-temperature heating, and high-pressure application. 2- At the same time as removing 311, 2- H on the site where 311 was removed - 321 can be injected and the desired amount of O 2- 311 is H - This method for producing an oxyhydride 340 can be easily produced, which is a thermodynamically metastable substance that cannot be obtained by a normal solid-state reaction. In particular, by applying a high pressure of, for example, several GPa, the hydrogen solid solubility in the oxide 310 can be rapidly increased. Under such high pressure, H - Conductor 320 to H - This allows the metal to be electrochemically diffused between solids without being vaporized as hydrogen gas, smoothly promoting the hydrogenation reaction of the oxide 310. Such a material synthesis technology that combines high-pressure application and electrochemistry has not been reported to date.

[0061] <Fourth embodiment> [Intercalation compounds] In the intercalation compound according to the fourth embodiment, metal ions are introduced into a compound having a van der Waals gap in its structure (van der Waals compound), such as a compound having a layered structure or a fibrous substance. These van der Waals compounds and metal ions have been described above.

[0062] [Method for producing intercalation compound] As shown in FIG. 38A , first, for example, a metal ion conductor 420 is brought into contact with a single-crystal van der Waals compound 410. If necessary, a metal ion source, such as an electrode made of this metal, may be brought into contact with the surface of the metal ion conductor 420 opposite the van der Waals compound 410, and metal ions may be supplied from this electrode to the metal ion conductor 420. Next, as shown in FIG. 38B , in this state, a voltage of such polarity that metal ions 421 of the metal ion conductor 420 move to the van der Waals compound 410 is applied between the van der Waals compound 410 and the metal ion conductor 420. Specifically, a voltage V is applied such that the potential of the metal ion conductor 420 is higher than that of the van der Waals compound 410. Heat treatment is then performed under high pressure, thereby injecting the metal ions 421 from the metal ion conductor 420 into the van der Waals compound 410. In this manner, an intercalation compound 430 containing the metal ions 421 can be produced. The temperature for this heat treatment is appropriately selected depending on the compound 410, etc., and is, for example, 300°C or more and 1000°C or less, typically 400°C or more and 700°C or less. The heat treatment time is also appropriately selected taking into consideration the size of the van der Waals compound 410, the heat treatment temperature, etc., and generally needs to be longer as the size of the compound 410 increases, but is, for example, 5 hours or more and 10 days or less, typically 10 hours or more and 3 days or less. The pressure during the heat treatment is, for example, 0.5 GPa or more and 10 GPa or less.

[0063] Example 4 In Example 4, a case will be described in which Mg ions are introduced into TaS2, which is a type of transition metal dichalcogenide, and used as the van der Waals compound 410. Figure 39A shows the structure of TaS2 before the introduction of Mg ions, and Figure 39B shows the structure of Mg-ion-containing TaS2 after the introduction of Mg ions.

[0064] A disk-shaped single crystal of TaS2 with a diameter of 4.3 mm and a thickness of 0.3 mm was used as the van der Waals compound 410. In a sample chamber of a high-pressure solid-state electrochemical cell similar to that of Example 2, single crystal TaS2, an Mg ion conductor, and an Mg electrode for supplying Mg ions were stacked in this order from the bottom on a Ti electrode, a carbon electrode was provided on the top layer, and the first lid 160 was closed. As the Mg ion conductor, a Mg 0.35 Zr 1.7 Nb 0.3 (PO4)3 was used. The Mg electrode was a cylindrical one with a diameter of 4.3 mm and a thickness of 1.0 mm. A positive voltage was applied to the first voltage application terminal 161 relative to the second voltage application terminal 171 so that a current of 1 mA would flow. A current was passed between the first current introduction terminal 140 and the second current introduction terminal 150 using a heating power supply, and the substrate was heated to 750°C using a carbon heater. Furthermore, six surfaces of the substrate 130 were pressed with high-pressure anvils 201-204, etc., to apply a high pressure of 1 GPa, and the substrate was treated for 40 hours. Figure 40 shows a photograph of a cross section of the treated sample. From Figure 40, it is clear that the Mg x Thus, Mg ion-containing TaS2, i.e., Mg x TaS2 was obtained. To date, there have been no reports of Mg ions, a divalent ion, being introduced into TaS2. For comparison, Figure 41 shows a photograph of the cross section of a sample that was processed without applying a voltage. As shown in Figure 41, no clear intercalation of Mg ions was observed when no voltage was applied.

[0065] Example 5 In Example 5, a case will be described in which MoTe2, which is a type of transition metal dichalcogenide, is used as the van der Waals compound 410 and Ag ions are introduced into this MoTe2.

[0066] A disk-shaped single crystal MoTe2 with a diameter of 4.3 mm and a thickness of 1.0 mm was used as the van der Waals compound 410. In a sample chamber of a high-pressure solid-state electrochemical cell similar to that of Example 2, the single crystal MoTe2, an Ag ion conductor, and an Ag electrode for supplying Ag ions were stacked in this order on a Ti electrode from the bottom up, with a carbon electrode on the top layer, and the first lid 160 was closed. The Ag ion conductor was AgI with a diameter of 4.3 mm and a thickness of 3.5 mm. A cylindrical Ag electrode with a diameter of 4.3 mm and a thickness of 0.5 mm was used. Then, a positive voltage was applied to the first voltage application terminal 161 relative to the second voltage application terminal 171 using a high-voltage solid-state electrochemical power supply so that a current of 0.5 mA was flowing. A current was then passed between the first current introduction terminal 140 and the second current introduction terminal 150 using a heating power supply, and the support 130 was heated to 400 to 460°C using a carbon heater. Furthermore, a high pressure of 1 GPa was applied by pressing the six surfaces of the support 130 with high-pressure anvils 201 to 204, etc., and the support 130 was treated for 40 hours. Figure 42A shows a photograph of the treated sample. Figure 42B shows the results of an analysis of Ag by fluorescent X-ray analysis. From Figure 42B, Ag concentrations of x=0.17 to 0.21 were found. x It can be seen that MoTe2 is obtained. In this way, Ag ion-containing MoTe2, i.e., Ag x MoTe2 was obtained. To date, there have been no reports of Ag ions being introduced into MoTe2.

[0067] Example 6 In Example 6, a case will be described in which MoTe2, which is a type of transition metal dichalcogenide, is used as the van der Waals compound 410 and Cu ions are introduced into this MoTe2.

[0068] A disk-shaped single crystal MoTe2 with a diameter of 4.3 mm and a thickness of 1.0 mm was used as the van der Waals compound 410. Then, in a sample chamber of a high-pressure solid-state electrochemical cell similar to that of Example 2, the single crystal MoTe2, a Cu ion conductor, and a Cu electrode for supplying Cu ions were stacked in this order on a Ti electrode from the bottom up, with a carbon electrode on the top layer, and the first lid 160 was closed. The Cu ion conductor was CuI with a diameter of 4.3 mm and a thickness of 3.5 mm. A cylindrical Cu electrode with a diameter of 4.3 mm and a thickness of 0.5 mm was used. Then, a positive voltage was applied to the first voltage application terminal 161 relative to the second voltage application terminal 171 using a high-voltage solid-state electrochemical power supply so that a current of 0.2 mA flowed. A current was then passed between the first current introduction terminal 140 and the second current introduction terminal 150 using a heating power supply, and the support 130 was heated to 400°C using a carbon heater. Furthermore, a high pressure of 1 GPa was applied by pressing the six surfaces of the support 130 with high-pressure anvils 201-204, etc., and the support 130 was treated for 20 hours. Figure 43A shows a photograph of the treated sample. Figure 43B shows the results of a Cu analysis using fluorescent X-ray analysis. From Figure 43B, Cu at x=0.10-0.64 was detected. x It can be seen that MoTe2 is obtained. In this way, Cu ion-containing MoTe2, i.e., Cu x MoTe2 was obtained. Until now, there have been no reports of Cu ions being introduced into MoTe2. Figure 44 shows the Cu ions obtained in this way. x The measurement results of the electronic conductivity of MoTe2 were compared with those of Ag obtained in Example 5. x The results of measurements of the electronic conduction properties of MoTe2 and MoTe2 are also shown. x MoTe2 has 10 times the electron conductivity at room temperature compared to MoTe2. 5 The degree of improvement is almost 0.2. x MoTe2 has 10 times better electron conduction properties than MoTe2. 4 It is clear that there has been some improvement.

[0069] As described above, according to the fourth embodiment, metal ions 421 can be injected from the metal ion conductor 420 into the van der Waals compound 410 by high-pressure solid-state electrochemistry using voltage application, high-temperature heating, and high-pressure application, and an intercalation compound 430 containing a desired amount of metal ions 421 can be easily produced.

[0070] Fifth Embodiment [Method for producing intercalation compound] In the method for producing an intercalation compound according to the fifth embodiment, a powder of a van der Waals compound and a powder of an alkaline earth metal hydride are mixed, and the resulting mixed powder is fired to produce an intercalation compound containing an alkaline earth metal.

[0071] The van der Waals compound and alkaline earth metal hydride have been described above. The calcination temperature can be appropriately selected depending on the van der Waals compound and alkaline earth metal hydroxide used, and is, for example, 300°C to 800°C, typically 500°C to 700°C. The calcination time can also be appropriately selected depending on the van der Waals compound and alkaline earth metal hydroxide used, and is, for example, 1 hour to 20 hours °C, typically 2 hours to 10 hours. Calcination may be performed at normal pressure or under high pressure. When calcination is performed under high pressure, volatilization of the raw materials during calcination can be prevented. When calcination is performed under high pressure, the pressure is, for example, 0.5 GPa to 10 GPa.

[0072] Example 7 In Example 7, TaS2 was used as the van der Waals compound and MgH2 was used as the alkaline earth metal hydride. TaS2 powder and MgH2 powder were mixed, and the resulting mixed powder was sintered at 600 °C under a high pressure of 1 GPa for 4 hours. As a result, Mg ion-containing TaS2, i.e., Mg x TaS2 was obtained.

[0073] Figure 45 shows the Mgx The results of measuring the X-ray diffraction pattern of TaS2 are shown in Figure 45. As shown in Figure 45, the 002 diffraction peak of TaS2 shifts to the lower angle side as x increases.

[0074] According to the fifth embodiment, an intercalation compound containing an alkaline earth metal can be easily produced by firing a mixed powder consisting of a van der Waals compound powder and an alkaline earth metal hydride powder.

[0075] Although the embodiments and examples of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments and examples, and various modifications based on the technical concept of the present invention are possible.

[0076] For example, the numerical values, materials, shapes, arrangements, etc. given in the above-described embodiments and examples are merely examples, and different numerical values, materials, shapes, arrangements, etc. may be used as necessary. [Explanation of symbols]

[0077] 10...Na ion-containing type II group IV clathrate compound, 11...Na ion, 20...Na ion conductor, 30...Na ion-extracted type II group IV clathrate compound, 50...NaAlB 14 Crystal, 51...Na ion, 60...Na ion conductor, 70...Na ion extraction NaAlB 14 Crystal, 110... sample chamber, 120... heater, 130... support, 140... first current introduction terminal, 150... second current introduction terminal, 160... first lid, 161... first voltage application terminal, 170... second lid, 171... second voltage application terminal, 180... temperature control circuit, 190... voltage application circuit, 310... oxide, 311... O 2- , 320…H - Conductor, 321...H - , 330...O 2- Conductors, 340...acid hydrides, 410...van der Waals compounds, 420...metal ion conductors, 421...metal ions

Claims

1. An ion-removing compound in which Na ions have been removed from NaAlB 14 to Na x AlB 14 (1>x≧0.06), a compound having a covalent skeletal structure in which the ions to be removed are most weakly bonded.

2. A method for producing an ion-extracting compound, comprising the steps of bringing a Na ion conductor into contact with NaAlB 14 , a compound having a covalent skeletal structure in which the ions to be extracted are most weakly bound, and then performing heat treatment under high pressure while applying a voltage to the NaAlB 14 and the Na ion conductor so that the NaAlB 14 side has a high potential, thereby extracting Na ions from the NaAlB 14 to Na x AlB 14 (1>x≧0.06).

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