(12) United States Patent (10) Patent No.: US 9.440,228 B2 H0s0no Et Al

USOO9440228B2

(12) United States Patent (10) Patent No.: US 9.440,228 B2 H0s0no et al. (45) Date of Patent: Sep. 13, 2016

(54) PEROVSKITE OXIDE CONTAINING (58) Field of Classification Search HYDRIDE ION, AND METHOD FOR CPC ...... BO1J 31 f(00 MANUFACTURING SAME See application file for complete search history. (75) Inventors: Hideo Hosono, Tokyo (JP); Hiroshi (56) References Cited Kageyama, Kyoto (JP); Yoji Kobayashi, Kyoto (JP); Mikio Takano, Kyoto (JP): Takeshi Yajima, Kyoto FOREIGN PATENT DOCUMENTS (JP) JP 2005-100978 A 4/2005 JP 2006-199578 A 8, 2006 (73) Assignee: JAPAN SCIENCE AND TECHNOLOGY AGENCY, (Continued) Kawaguchi-shi (JP) OTHER PUBLICATIONS (*) Notice: Subject to any disclaimer, the term of this Kobayashi et al(An oxyhydride of BaTiO3 exhibiting hydride patent is extended or adjusted under 35 exchange and electronic conductivity, Nature Materials, vol. 11, U.S.C. 154(b) by 245 days. (2012) pp. 507-511 published online on Apr. 15, 2012).* (21) Appl. No.: 14/130,184 (Continued) (22) PCT Filed: Jul. 5, 2012 Primary Examiner — Melvin C Mayes (86). PCT No.: PCT/UP2012/067.157 Assistant Examiner — Michael Forrest (74) Attorney, Agent, or Firm — Westerman, Hattori, S 371 (c)(1), Daniels & Adrian, LLP (2), (4) Date: Dec. 30, 2013 (87) PCT Pub. No.: WO2013/008705 (57) ABSTRACT Problem Many oxide-ion conductors exhibit high func PCT Pub. Date: Jan. 17, 2013 tionality at high temperatures due to the large weight and (65) Prior Publication Data charge of oxide ions, and it has been difficult to achieve the functionality at low temperatures. US 2014/O128252 A1 May 8, 2014 Solution. A perovskite oxide having hydride ion conduc tivity, at least 1 at % of the oxide ions (O) contained in a (30) Foreign Application Priority Data titanium-containing perovskite oxide being Substituted with hydride ions (H). This oxide, in which negatively charged Jul. 8, 2011 (JP) ...... 2011-151738 hydride ions (H) are used for the ionic conduction, has both (51) Int. Cl. hydride ion conductivity and electron conductivity. As a BOI 39/02 (2006.01) starting material, the titanium-containing perovskite oxide is BOI. 23/00 (2006.01) kept together with a powder of an alkali metal or alkaline earth metal hydride selected from LiH, Cah, SrH, and (Continued) BaH in a temperature range of 300° C. or higher and lower (52) U.S. Cl. than the melting point of the hydride in a vacuum or an inert CPC ...... B01J 39/02 (2013.01); B01J 23/002 gas atmosphere to Substitute some of the oxide ions in the (2013.01); B01J 23/02 (2013.01); COIB 3/001 oxide with the hydride ions, resulting in the introduction of (2013.01); the hydride ions into oxygen sites. (Continued) 6 Claims, 5 Drawing Sheets

US 9,440.228 B2 Page 2

(51) Int. Cl. Ohkoshi, Shin-ichi, et al., “Synthesis of metal oxide with a room COIB 3/00 (2006.01) temperature photoreversible phase transition’. Nature Chemistry, COIB 3/50 (2006.01) Macmillan Publishers Limited., 2010, vol. 2, pp. 539-545, cited in COIG 23/00 (2006.01) Specification. HOLM 4/90 (2006.01) Gong, Wenhe, et al., "Oxygen-Deficient SrTiO3-X, X = 0.28, 0.17. BOI. 23/02 (2006.01) and 0.08. Crystal Growth, Crystal Structure, Magnetic, and Trans port Properties”, Journal of Solid State Chemistry 90, Academic (52) U.S. Cl. Press, Inc., 1991, pp. 320-330, cited in Specification. CPC ...... COIB 3/503 (2013.01); COIG 23/003 Steinsvik, Svein, et al., “Hydrogen ion conduction in iron-substi (2013.01); COIG 23/005 (2013.01); COIG tuted strontium titanate, SrTi1-xFexO3-X/2(0sxs0.8), Solid State 23/006 (2013.01); H0IM 4/9033 (2013.01); Ionics 143, Elsevier Science B.V., 2001, pp. 103-116. cited in COIP 2002/34 (2013.01); COIP 2002/72 Specification. (2013.01); COIP 2004/52 (2013.01); COIP Hayashi, Katsuro, et al., “Light-induced conversion of an insulating 2006/32 (2013.01); COIP 2006/40 (2013.01); refractory oxide into a persistent electronic conductor'. Nature, Y02E 60/324 (2013.01); Y02E 60/50 (2013.01) Nature Publishing Group, Oct. 3, 2002, vol. 419, pp. 462-465, cited in Specification. (56) References Cited Malaman, B. et al., “Etude structurale de l’hydruro-oxyde LaHO par diffraction des rayons X et par diffraction des neutrons'. Journal of FOREIGN PATENT DOCUMENTS Solid State Chemistry 53, Academic Press Inc., 1984, pp. 44-54, cited in Specification. JP 2007-220406 A 8, 2007 Hayward, M. A., et al., “The Hydride Anion in an Extended JP 4219821 B2 2, 2009 Transition Metal Oxide Array: LaSrCoO 3H0.7”. Science, Ameri JP 4374631 B2 12/2009 can Association for the Advancement of Science, USA, 2002, vol. WO 03-089373 A1 10, 2003 295, pp. 1882-1884, cited in Specification. WO 2010/105787 A1 9, 2010 Bridges, Craig, A., et al., “Observation of Hydride Mobility in the OTHER PUBLICATIONS Transition-Metal Oxide Hydride LaSrCoO3H0.7”. Advanced Mate rials, Wiley-VCH Verlag GmbH & Co. kGaA. Weinheim, 2006, 18, Yajima et al.(Epitaxial Thin Films of ATiO3-xHx (A = Ba, Sr, Ca) pp. 3304-3308, cited in Specification. with Metallic Conductivity, JAm Chem Soc 2012, 134, 8782-8785 Helps, Rebecca, M., et al., “Sr3Co2O4.33HO.84: An Extended Tran published on May 7, 2012).* sition Metal Oxide-Hydride'. Inorganic Chemistry, American Poeppelmeier (A Mixed Oxide-Hydride Perovskite, Science, vol. Chemical Society, 2010,49, pp. 11062-11068, cited in Specification. 295 (2002) p. 1849).* Waser, R. “Solubility and diffusivity of hydrogen defects in Poulsen (Speculations on the existence of hydride ions in proton BaTiOO3 ceramics, Science of Ceramics', 1988, vol. 14, pp. 383 conducting oxides, Solid State Ionics 145 (2001) 387-397).* 388, cited in ISR. International Search Report, dated Oct. 2, 2012, corresponding application No. PCT/JP2012/067157. * cited by examiner U.S. Patent Sep. 13, 2016 Sheet 1 of 5 US 9,440.228 B2

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03 50 100 50 20 Time (min) U.S. Patent Sep. 13, 2016 Sheet 2 of 5 US 9,440,228 B2

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U.S. Patent Sep. 13, 2016 Sheet 4 of 5 US 9,440.228 B2

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: c 2.0- : r o 0.5, '' too o so too so soo Temperature (°C) US 9,440,228 B2 1. 2 PEROVSKITE OXDE CONTAINING which hydride ions are inserted into an oxide in an amount HYDRIDE ION, AND METHOD FOR exceeding the amount of oxygen defects are limited to only MANUFACTURING SAME a small number of Substances that use typical elements. Examples of such substances include LaHO (NPL 4) and TECHNICAL FIELD 12CaO.7AlO, (NPL 5 and PTL 4). In 2002, M. A. Hayward et al. succeeded in synthesizing The present invention relates to a titanium-containing a cobalt oxide-hydride containing hydride ions, perovskite oxide, in particular, a titanium-containing per LaSrCoO.H., (NPL 6). After that, in 2006, C. A. Bridges et ovskite oxide having hydride ion conductivity, a method for al. reported the diffusion phenomenon of hydride ions in the manufacturing the oxide, and the use of the oxide. 10 cobalt oxide LaSrCoO.H., (NPL 7). This indicates that hydride ions in the substance have mobility, but does not BACKGROUND ART indicate a chemical reaction with the ambient atmosphere For example, titanium-containing oxides having a per (e.g., gaseous phase). The ion conductivity is unknown. ovskite crystal structure or a layered perovskite crystal 15 Furthermore, R. M. Helps et al. reported a cobalt oxide structure, which are represented by MTiO, (M. represents hydride having a structure similar to that of the Substance, Ca, Ba, Mg, Sr., or Pb) and titanium-containing oxides in SrCo-OHols (NPL 8). These two Substances are the first which some of Tiatoms are substituted with at least one type examples in which a large amount of hydride ions were of Hf and Zr (PTL 1) (collectively referred to as "titanium taken into a transition metal oxide. containing perovskite oxides') have a considerably high PTL 1: Japanese Unexamined Patent Application Publica relative dielectric constant. Therefore, the titanium-contain tion No. 2006-199578 ing perovskite oxides have been eagerly studied for a long PTL 2: Japanese Patent No. 4374631 time as devices such as capacitor materials and dielectric PTL 3: Japanese Unexamined Patent Application Publica films and also in terms of applications to Substrate materials tion No. 2005-100.978 of other perovskite transition metal oxides and nonlinear 25 PTL 4: Japanese Patent No. 4219821 resistors. NPL 1: S. Ohkoshi et al., “Nature Chemistry’ 2, p. 539-545 In addition to the excellent characteristics, the fact that (2010) titanium is an element which has a low environmental load, NPL 2: W. Gong et al., “Journal of Solid State Chemistry” is safe for living bodies, and is abundant on the earth 90, p. 320-330 (1991) facilitates the use of titanium-containing perovskite oxides 30 NPL 3: S. Steinsvik et al., “Solid State Ionics' 143, p. for biocompatible materials and the industrial use of tita 103-116 (2001) nium-containing perovskite oxides for electronic materials, NPL 4: K. Hayashi et al., “Nature” 419, p. 462-465 (2002) optical materials, and the like. Among Clarke numbers, NPL 5: B. Malaman, J. F. Brice, Journal of Solid State which represent the proportions of elements present in the Chemistry” 53, p. 44-54 (1984) earth’s crust, titanium is in tenth place among all elements 35 NPL 6: M. A. Hayward et al., “Science 295, p. 1882-1884 and in second place after iron among transition metals. (2002) It is known that titanium compounds in which the NPL 7: C. A. Bridges et al., “Advanced Materials' 18, p. valences of Ti are +4 (3d) and +3 (3d) are stably present. 3304-3308 (2006) The material development of titanium-containing oxides NPL 8: R. M. Helps et al., “Inorganic Chemistry” 49, p. that uses the conductivity of such d electrons has been 40 11062-11068 (2010) eagerly conducted. For example, Nb-doped anatase (TiO) is promising as a transparent electrode material, and TiO, SUMMARY OF INVENTION known as one of Magneli phases is promising as a Switching material (NPL 1) because TiO, exhibits a metal-insulator Technical Problem transition. 45 It is known that, by forming oxygen defects (vacancies) in The most developed ion conductor that uses negative ions an insulative titanium-containing perovskite oxide, that is, is an oxide-ion conductor. However, many oxide-ion con by doping the insulative titanium-containing perovskite ductors exhibit high functionality at high temperatures due oxide with electrons, a mixed valence state with titanium to the large weight and charge of oxide ions, and it has been having Valences of +3 and +4 is achieved and thus the 50 difficult to achieve the functionality at low temperatures. As insulative titanium-containing perovskite oxide can be con a result of the recent depletion of petroleum resources and verted into a material with low electrical resistance (NPL 2). the recent demand for improving environmental pollution, To achieve this, various methods such as a heat treatment at opportunities for effectively using hydrogen resources high temperature in vacuum, in hydrogen, in nitrogen, or in which provide clean energy have been increasing. Thus, the argon gas, using an oxygen getter are employed. 55 development of ion conductors that use hydride ions and are Regarding oxides, an increasing number of studies have composed of elements safe for living bodies has been been conducted on, for example, an oxide-ion mixed con demanded. ductor (PTL 2) and an electrochemical device including a Since applications such as an electrode are considered to material having proton (H) ion conductivity as a Solid have both ion conductivity and electron conductivity, a electrolyte (PTL 3). On the other hand, almost no studies 60 Substance containing a transition metal is required. Cobalt have been conducted on negatively charged hydride ions has a valence of 2 or more in typical oxides. However, in the (H). The possibility that hydrogen in an oxide is conducted cobalt oxide-hydrides, which are only examples shown in in the form of hydride ions was proposed by S. Steinsvik et PTLS 6 and 7, cobalt is in an extremely low oxidation state al. in 2001 (NPL 3). However, there are opposing opinions with monovalent ions and thus the cobalt oxide-hydrides are on this theory and its validity is still disputed. 65 unstable. Theoretical calculation has shown that the d elec In general, the compatibility between oxide ions and trons of cobalt are localized, and thus there is no electron hydride ions is very poor. Therefore, Successful examples in conductivity. Furthermore, cobalt is a rare metal and has US 9,440,228 B2 3 4 toxicity in some cases. These facts pose a problem when may be difficult to combine a material in an abnormally low cobalt is applied to an electrode or the like. valence state, such as cobalt in a cobalt oxide-hydride, with Transition metal oxides are considered to be applied to, other materials. However, the Ti-containing perovskite for example, batteries that use the conduction of hydride oxide-hydride of the present invention has a mixed valence ions. To achieve this, a transition metal oxide having both 5 state in which the Valences of titanium are +3 and +4, and ion conductivity and electron conductivity is required. How therefore is easily combined with other materials using ever, known cobalt oxide-hydrides have many disadvanta electron conductivity. geous factors such as the rarity of cobalt ions, toxicity, the instability derived from an extremely low oxidation state Advantageous Effects of Invention with monovalent ions, and the lack of electron conductivity 10 due to strong electron correlation. Therefore, a hydride The present invention provides a specific compound that ion/electron mixed conductor that is composed of a metal uses, for ion conduction, negatively charged hydride ions oxide containing an abundant element having a stable oxi (H) which have received scant attention, that is, an oxide in dation number, such as titanium, needs to be developed. In which some of oxide ions (O) of a titanium-containing addition, a novel ceramic material having excellent hydro 15 perovskite oxide are substituted with hydride ions. Since this gen absorption/desorption characteristics needs to be devel oxide is an environmentally-friendly inexpensive titanium oped in order to effectively use hydrogen. based oxide and has excellent characteristics such as mixed conductivity including both hydride ion conductivity and Solution to Problem electron conductivity, the oxide is useful as a material for electronic devices that can exhibit functionality at low The inventors of the present invention have found that a temperatures. Furthermore, the oxide is useful as a novel Ti-containing perovskite oxide can take in hydride ions (H) hydrogen absorption/desorption material. in a low concentration to a high concentration under par ticular heat treatment conditions; the obtained Ti-containing BRIEF DESCRIPTION OF DRAWINGS perovskite oxide containing hydride ions has both hydride 25 ion conductivity and electron conductivity; and the obtained FIG. 1 illustrates the crystal structure (left) of BaTiO, Ti-containing perovskite oxide containing hydride ions has before a heat treatment and the crystal structure (right) of a excellent characteristics such as reactivity with an outside sample a after the heat treatment in Example 1. hydrogen gas at a low temperature of about 450° C. or lower, FIG. 2 illustrates change in the concentrations of H and that is, ion conductivity. The Ti-containing perovskite oxide 30 HD detected in a gaseous phase when the sample a in containing hydride ions is defined as “a Ti-containing per Example 1 was heated-up from room temperature while ovskite oxide-hydride'. The present invention is as follows. deuterium was caused to flow. The present invention is a perovskite oxide having FIG. 3 illustrates the neutron diffraction intensity (top) hydride ion conductivity, which has a novel composition that and the calculation pattern (bottom) of the sample a in provides specific and useful characteristics. In the perovskite 35 Example 1 and a sample b after the heat treatment in a oxide, 1 at. '% or more of oxide ions contained in a deuterium gas in terms of typical diffraction peaks. titanium-containing perovskite oxide are Substituted with FIG. 4 illustrates change in the electrical resistances of hydride ions (H). single crystal thin films in Example 2 as a function of The oxide can be manufactured in the form of powder by temperature. preparing a titanium-containing perovskite oxide powder as 40 FIG. 5 illustrates the crystal structures (left) of Sr TiO, a starting material and keeping the titanium-containing and Sr TiO, before a heat treatment and the crystal struc perovskite oxide powder together with a powder of an alkali tures (right) of the samples after the heat treatment in metal or alkaline-earth metal hydride selected from lithium Example 3. hydride (LiH), calcium hydride (CaH), strontium hydride FIG. 6 illustrates change in the concentration of H gas of (SrH), and barium hydride (BaFI) in a temperature range 45 the samples after the heat treatment in Example 3, the H gas of 300° C. or higher and lower than a melting point of the being detected with a quadrupole mass spectrometer. hydride in a vacuum or an inert gas atmosphere to Substitute FIG. 7 illustrates the crystal structure (left) of EuTiO, some of oxide ions in the oxide with hydride ions. before a heat treatment and the crystal structure (right) of the The oxide can also be manufactured in the form of a thin sample after the heat treatment in Example 4. film by preparing a titanium-containing perovskite oxide 50 FIG. 8 illustrates change in the concentration of H gas of thin film as a starting material and keeping the titanium the samples after the heat treatment in Example 4, the H gas containing perovskite oxide thin film together with a powder being detected with a quadrupole mass spectrometer. of an alkali metal or alkaline-earth metal hydride selected from lithium hydride (LiH), calcium hydride (CaH), stron DESCRIPTION OF EMBODIMENTS tium hydride (Srh), and barium hydride (BaFI) in a 55 temperature range of 300° C. or higher and lower than a Perovskite oxides are generally represented by ABO, melting point of the hydride in a vacuum or an inert gas ABO, and ABO7. These oxides are collectively repre atmosphere to Substitute some of oxide ions in the oxide sented by General formula A.B.O. (where n represents with hydride ions. 1, 2, or OO). In the present invention, a starting material This oxide is useful as a mixed conductor having both 60 contains Ti as the B component and can be represented by hydride ion conductivity and electron conductivity. A Formula I below. (Formula I) MTiO (where n rep ceramic electrode requires the permeability of hydrogen ions resents 1, 2, or OO). That is, when n=1, the starting material and electron conductivity, but this oxide can be used as a is MTiO. When n=2, the starting material is MTiO,. hydrogenation catalyst and an electrochemical device Such When n=OO, the starting material is substantially MTiO. M as a hydrogen electrode, a hydrogen permeation membrane, 65 typically represents at least one of Ca, Ba, Sr., Pb, and Mg, or a hydrogen gas sensor. This oxide can also be used as a but is not limited to these divalent positive ions. The starting hydrogen absorption/desorption material. Furthermore, it material can be a solid solute containing cations having US 9,440,228 B2 5 6 different Valences, such as La and Na, and can contain limited. The time required for the heat treatment may be deficient. The Ti site may also be partly substituted with about one hour or longer though depending on the tempera another transition metal such as Hf or Zr. ture. The starting material is preferably in the form of powder. The atmosphere containing the CaF2 powder may be In the case of MTiO, the starting material may be in the created by simultaneously vacuum-sealing the CaF2 powder form of a thin film deposited on a substrate. Any substrate and the powder compact of MTiO or the thin film composed of a material that withstands a heat treatment sample serving as the starting material in a thermally and temperature may be used as the substrate for the MTiO, thin chemically durable container Such as quartz glass or a film. The MTiO, thin film may be a single crystal thin film stainless steel tube. The atmosphere in the sealed tube may 10 be an inert gas such as argon or nitrogen instead of vacuum. or a polycrystalline thin film. A substrate suitable for the The reaction may be caused while performing vacuuming MTiO single crystal thin film is a (LaAlO). using a vacuum pump. However, since the ionic hydride (SrAl Taos.O.), (abbreviated as LSAT) Substrate. Such as CaH Strongly reacts with water, it is required that The starting material MTiO is synthesized by moisture is not continuously supplied to the atmosphere in causing a solid-phase reaction of a raw material containing 15 the sealed tube through a channel of the vacuum pump. The M and Ti at an atomic equivalent ratio of n+1 in in the air or oxygen gas and moisture present in a reaction system in the an oxidizing atmosphere at a firing temperature of 800° C. sealed tube before the reaction can be removed by using an or higher and lower than 1500° C. The raw material is excessive amount of CaH that reacts with the oxygen gas typically a carbonate of M and titanium oxide. The starting and moisture. material can also be obtained by a method that uses an CaH and MTiO exhibit high reactivity when they aqueous Solution, Such as a hydrothermal method or a are in contact with each other in the container, but still sol-gel method. These methods are publicly known and can exhibits reactivity when they are not in contact with each be appropriately employed. The starting material is also other. In the case where they are not in contact with each available in market in the form of powder. other, the temperature of a position at which the The MTiO, thin film is formed on a substrate such as an 25 MTiO is inserted and the temperature of a position LSAT substrate by a pulsed laser deposition (PLD) method at which the CaH is inserted can be independently con using an MTiO sintered body as a target. The film formation trolled. The reaction can be caused to proceed while pre method is not limited to the PLD method, and a vapor venting the decomposition of the MTiO, and thus the deposition method such as a sputtering method or a plasma temperature of the position at which the CaFI is inserted can splaying method can also be used. These methods are also 30 be increased to near the melting point of Cah. Note that, when CaH and MTiOs are not in contact with each publicly known and can be appropriately employed. other, a longer time is required for the heating. An alkali metal or alkaline-earth metal hydride selected The CaH reacts with oxygen contained in the from lithium hydride (LiH, melting point 680° C.), calcium MTiOs to form calcium oxide (CaO). This formation hydride (CaH, melting point 816° C.), strontium hydride 35 causes hydrogenation in which hydrogen atoms generated as (SrH. melting point 675° C.), and barium hydride (Bah. a result of the decomposition of the CaH occupy all or some melting point 675°C.) is used to extract some of oxide ions of oxygen vacancies formed in the MTiO, and at the contained in the starting material and Substitute the oxide same time a hydrogen gas is generated in the reaction ions with hydride ions (H). These hydrides have similar atmosphere. characteristics in the form of ionic hydrides. The reason why 40 The oxygen extraction from the MTiO, and the the ionic hydrides can be used to substitute oxide ions with hydrogenation reaction in the MTiO proceed more hydride ions is considered to be as follows. These substances quickly as the amount of CaH used increases, the heat have not only the capability to extract oxygen from a treatment time lengthens, and the heat treatment temperature Ti-containing perovskite oxide but also the capability to increases. The oxygen extraction and the hydrogenation Supply hydride ions to oxygen sites from which oxygen has 45 reaction can also be caused to proceed quickly by decreasing been extracted, even in the case where heating is performed the size of the MTiO powder sample or decreasing in a solid State, that is, at a low temperature equal to or lower the thickness of the MTiO, thin film. When the amount of than the melting point. Therefore, hydride ions are inserted CaH is not sufficiently large, the heat treatment time is without introducing oxygen defects in the starting material short, or the heat treatment temperature is low, the oxygen in advance. In the manufacturing method of the present 50 extraction and the hydrogenation reaction proceed slowly invention, an insertion/substitution reaction of hydride ions and thus an MTiOs oxide containing high-concentra produced as a result of the dissociation of the ionic hydride tion hydride ions cannot be produced. As described above, occurs at a relatively low temperature, and thus the structural the amount of hydrogen taken into the MTiO varies skeleton of the starting material is not broken. Furthermore, depending on the factors such as the amount of Cah, the a deoxidation reaction and an insertion reaction of a large 55 heat treatment time, the heat treatment temperature, the size amount of hydride ions can be topochemically achieved at of particles, and the form. Therefore, these factors are the same time, which provides an easy manufacturing pro referred to as “hydridization-ability-determining factors'. CCSS, If the heat treatment temperature exceeds 650° C., the Hereinafter, the case where a CaM powder is used will be MTiO decomposes and an impurity Such as TiH is described, but the above-described other hydride powders 60 generated. Therefore, a single-phase MTiO oxide can also be used. The MTiOra-i-l powder or the MTiO containing hydride ions cannot be formed. As described in thin film serving as the starting material is heat-treated by Examples, the sample BaTiO before the heat treatment has, being kept in an atmosphere containing a CaM powder at at room temperature, a tetragonal perovskite structure which 200° C. or higher and lower than the melting point (81.6°C.) is distorted from an ideal cubic perovskite structure because of CaM, desirably 300° C. or higher and 600° C. or lower 65 of the ferroelectricity caused by the unoccupied d orbitals of and then cooled to room temperature. The temperature titanium. On the other hand, the sample after the heat increasing rate and the temperature-decreasing rate are not treatment has only a cubic perovskite structure at room US 9,440,228 B2 7 8 temperature because electrons are injected to the d orbitals invention compared with common oxide-ion conductors. of titanium through the substitution between oxide ions and This is because hydride ions (H) are lighter than oxide ions hydride ions. (O) and the charge of the hydride ions is half the charge As the heat treatment time lengthens, the amount of and of the oxide ions. The exchange reaction proceeds more thus the amount of calcium oxide generated increases. The 5 quickly as the amount of hydride ions contained in the reaction proceeds as long as an excessive amount of CaH2 oxide-hydride increases and the heating temperature is present, but hydrogen cannot be inserted in a concentra increases. At a heating temperature equal to or higher than tion that exceeds the maximum concentration in which the threshold temperature that is determined by the type of hydrogen can be taken in the MTiO. Through the above heat treatment, up to 20 at. '% of oxygen can be 10 M and the value n in the MTiO, the exchange substituted with hydrogen. When the amount of substituted reaction still proceeds, but the oxide starts to decompose. At oxygen is 1 at. 96 or more, the hydride ion conductivity can a heating temperature lower than the threshold temperature, be achieved. The hydride ion conductivity increases in the hydrogen concentration in the oxide-hydride does not proportion to the amount of Substituted oxygen. Therefore, change, but a slight amount of hydrogen may be desorbed. 5 at. '% or more of oxygen is preferably substituted and 10 15 The Ti-containing perovskite oxide-hydride of the present at. 96 or more of oxygen is more preferably substituted. invention can also be used as a hydrogen absorption/des In the case of the powder sample, the hydrogen concen orption material. When the temperature of the Ti-containing tration in the MTiO oxide can be determined by perovskite oxide-hydride is increased in an atmosphere not powder X-ray diffraction, powder neutron diffraction, a containing a hydrogen gas, a hydrogen gas is desorbed at decomposition experiment in an acid solution Such as HCl, 20 about 400° C. or higher. In general, in the hydrogenation of a combustion experiment in a reducing atmosphere, quadru alkenes and alkynes and the catalytic reaction in which pole mass spectrometry, or a change in magnetic suscepti methanol is synthesized from CO, a first stage at which a bility as a function of temperature. In the case of the thin film hydrogen molecule H is adsorbed and the hydrogen mol sample, the hydrogen concentration can be determined with ecule is dissociated into a single atom H is required. A a secondary ion mass spectrometer (SIMS). 25 precious metal such as Pt or Pd has been used to perform the The Ti-containing perovskite oxide-hydride obtained by above process. However, the Ti-containing perovskite the above-described method is a substance in which up to 20 oxide-hydride also generates a H species in a hydrogen gas. at.% of oxygen in oxygen sites is substituted with hydrogen. Therefore, the same catalytic activity is achieved with use of That is, the substance can be represented by Basic formula an inorganic material not containing a precious metal. The II below. 30 Substance after the hydrogen desorption can absorb hydro (Basic formula II) MTi(OH) (where M is the gen again through the reaction with CaF2 while keeping its same as that of the starting material, H represents hydride form. ions substituted for oxygen ions, 0.01sXs0.2, n represents The Ti-containing perovskite oxide-hydride of the present any one of 1, 2, and OO). invention exhibits high thermal stability and chemical sta The hydrogen subjected to the substitution randomly 35 bility. The Ti-containing perovskite oxide-hydride is stable (statistical manner) occupies oxygen sites. However, by in the air, stable against water and an alkali Solution, and controlling any of the hydridization-ability-determining fac even stable against boiling water. However, in a strong acid, tors, a gradient can be provided to the hydrogen concentra the Ti-containing perovskite oxide-hydride desorbs hydro tion distribution from the surface of the powder or thin film gen while being decomposed. to its center. 40 The electrical resistance of the obtained Ti-containing EXAMPLE 1. perovskite oxide-hydride decreases with increasing the con centration of hydride ions contained therein. In the case of The present invention will now be further described in the powder sample, it is difficult to qualitatively and quan detail based on Examples. Barium titanate (BaTiO) par titatively estimate the electrical resistance due to the contact 45 ticles having a particle size in the range of 100 nm to 200 nm resistance. In the case of the thin film sample, the Ti and synthesized by a synthesis method that uses a solution, containing perovskite oxide-hydride has an electrical resis such as a citric acid method, were heat-treated at about 200° tivity of 10° S.2cm or less at room temperature and exhibits C. to remove moisture attached to the surfaces of the positive temperature dependence, that is, a metallic behav particles. Subsequently, three equivalents of CaH2 powder ior. 50 and the BaTiO, particles were mixed with each other in a The Ti-containing perovskite oxide-hydride of the present glove box and molded into a pellet using a hand press. The invention is a mixed conductor having both hydride ion pellet was inserted into a quartz tube having an internal conductivity and electron conductivity. In terms of Such volume of about 15 cm and vacuum-sealed. Three samples characteristics, the Ti-containing perovskite oxide-hydride were heat-treated under the heat treatment conditions shown is useful for electrode catalysts and hydrogen permeation 55 in Table 1 to cause a hydrogenation reaction. The samples membranes of Solid-electrolyte fuel cells, hydrogen gas after the heat treatment were treated with a 0.1 M NHCl generating apparatuses that use water electrolysis, and the methanol solution to remove an unreacted Cah and a like and solid electrolytes of fuel cells and hydrogen gas by-product CaO that were attached to a product. SSOS. When the Ti-containing perovskite oxide-hydride 60 TABLE 1. obtained by the above method is heated to 300° C. or higher Heat treatment Heat treatment in an atmosphere containing a deuterium gas, the hydrogen Sample No. temperature ( C.) time (h) Composition in the oxide is exchanged for the deuterium gas in the 8. S8O 150 BaTi(OosHo2) atmosphere, and the deuterium is migrated in the oxide. b S4O 100 BaTi(OogHol)3 The exchange reaction with an outside hydrogen gas 65 C 500 100 BaTi(Oog7Hoo3)3 proceeds at a relatively low temperature of about 300° C. in the Ti-containing perovskite oxide-hydride of the present US 9,440,228 B2 9 10 The color of the samples washed with a 0.1 M NHCl Pa, and a KrF excimer laser pulse (wavelength=248 nm) was methanol solution is light blue under the conditions for the employed as an excitation light source. In a glove box filled hydrogenation reaction providing weak hydrogenation with Ar, the obtained single crystal thin film and 0.2 g of power and becomes black as stronger hydrogenation power CaH2 powder were vacuum-sealed in a quartz tube and is provided. The obtained samples were found to maintain a heat-treated at a temperature of 300° C. to 530° C. for one perovskite crystal structure by powder X-ray diffraction or day to cause a hydrogenation reaction. As in Example 1, an powder neutron diffraction. The samples a, b, and c before unreacted CaFI, and a by-product CaO that were attached to the heat treatment had, at room temperature, a tetragonal a product were removed by ultrasonic cleaning with acetone. perovskite structure which was distorted from an ideal cubic It was found from X-ray diffraction that the obtained perovskite structure because of the ferroelectricity. On the 10 sample was a single crystal thin film in which a perovskite other hand, the samples after the heat treatment had only a crystal structure was maintained. It was found from the cubic perovskite structure at room temperature. depth profile of thin films subjected to the hydrogenation It was confirmed by Rietveld analysis that the obtained reaction, the depth profile being measured by SIMS, that samples had the compositions shown in Table 1. Note that hydrogen was substantially uniformly distributed in all the there is a possibility that less than 5 at. '% of oxygen defects 15 thin film samples under the above-described heat treatment are present in each of the samples. It was confirmed by the conditions. The composition in the case of M=Sr provided measurement of (the Valence of titanium by) magnetic with reference data was found to be SrTiOssHos. The Susceptibility, the quadrupole mass spectrometry, the ther hydrogen contents of the thin film samples with M-Ba and mogravimetric analysis, and the decomposition experiment Ca subjected to the same heat treatment were substantially that the oxygen content and the hydrogen content in each of the same as that of the case of M=Sr. the samples that were determined by the diffraction experi It was found from the depth profile measured by SIMS ment were correct. FIG. 1 illustrates the determined crystal that, when the MTiO (M=Ba, Sr., or Ca) single crystal thin structure (right) of the sample a after the heat treatment film containing hydrogen (H) was kept in an atmosphere together with the crystal structure (left) of BaTiO, before the containing deuterium (D) at 400° C. for one hour, H in the heat treatment. In the BaTiO, after the heat treatment, some 25 MTiOs (M-Ba, Sr., or Ca) was completely substituted with of oxide ions are substituted with hydride ions. D. As in Example 1, this phenomenon indicates that It was also found that, also in other MTiO oxides hydride ions are capable of being conducted in a thin film. with M representing Ca, Sr. and Pb, the same hydrogenation FIG. 4 illustrates change in the electrical resistances of phenomenon occurred when the same heat treatment con these samples as a function of temperature from 2 K to 300 ditions were applied, that is, up to about 20 at. 96 of oxygen 30 K. The electrical resistances of all the samples decreased in oxygen sites was Substituted with hydrogen. with decreasing the temperature, that is, all the samples FIG. 2 illustrates change in the concentrations of H2 gas exhibited metallic temperature dependence, except that the and hydrogen deuteride (HD) gas detected with a quadru electrical resistance of the sample with M-Ca increased at a pole mass spectrometer when 1.2 g of the sample a was low temperature of 30 K or lower though the cause was heated from room temperature to 400° C. over about 160 35 unclear. The electrical resistivities of the samples with minutes while a gas (5 vol%, D/Ar) containing a deuterium M-Ca, Ba, and Sr at room temperature were 8x10 G2cm, gas was caused to flow at a flow rate of 30 mL/min. A trace 8x10 S2cm, and 2x10 G2cm, respectively. In perovskite amount of HD was detected from about 250° C. due to the oxides, ion conduction is quite unlikely to occur at Such a exchange between hydrogen in the sample and deuterium in low resistivity at room temperature. This indicates that the the gaseous phase. At a temperature exceeding 350° C., the 40 MTiO, (M-Ba, Sr. or Ca) is a mixed conductor that exhibits exchange rate Suddenly increased. not only hydride ion conduction at high temperatures, but FIG. 3 illustrates the neutron diffraction intensity (top) also considerably high electron conduction. and the calculation pattern (bottom) of the sample a and the sample b after the heat treatment in the deuterium gas. FIG. EXAMPLE 3 3 shows that hydrogen (H) in the sample a is quickly 45 exchanged for deuterium (D) not only on the Surface but Layered strontium titanate (Sr-TiO, and SrTi2O7) par also over the entire sample. This phenomenon indicates that ticles having a particle size of about 200 nm and synthesized hydride ions are capable of being conducted in a thin film. by a synthesis method that uses a solution, such as a citric The same phenomenon also occurred in other acid method, were subjected to vacuum drying at 120° C. to MTiO oxides with M representing Ca, Sr, and Pb. As 50 sufficiently remove moisture attached to the surfaces of the is clear from the measurement results of the electrical particles. Subsequently, three equivalents of CaH2 powder resistance of the sample obtained in Example 2 below, the and the Sr TiO, particles or six equivalents of CaH powder Ti-containing perovskite oxide-hydride of the present inven and the Sr TiO, particles were mixed with each other in a tion has high electron conductivity and thus it is difficult to glove box and molded into a pellet using a hand press. The measure the ion conductivity. However, the occurrence of 55 pellet was inserted into a Pyrex (registered trademark) tube the same phenomenon provides a clue as to the fact that the having an internal volume of about 15 cm and vacuum Ti-containing perovskite oxide-hydride has high ion con sealed. The sample was heat-treated at 480° C. for seven ductivity at high temperatures. days. The sample after the heat treatment was washed with a 0.1 M NHCl/methanol solution to remove a remaining EXAMPLE 2 60 unreacted CaH and a by-product CaO. The sample washed with a 0.1 M NHC1/methanol solu An MTiO (M=Ba, Sr., or Ca) single crystal thin film tion showed dark blue as in the case of BaTiOH or the having an area of 1 cmx1 cm and a thickness of 120 nm was like. The obtained sample was found to maintain a layered deposited as a sample on an LSAT substrate by a PLD perovskite crystal structure from powder X-ray diffraction or method described below. An MTiO (M=Ba, Sr., or Ca) pellet 65 powder neutron diffraction. was used as a target. The temperature of the Substrate was It was confirmed by Rietveld analysis that the obtained 700° C., the oxygen pressure during the deposition was 0.05 sample had the composition, Sr-TiOH or US 9,440,228 B2 11 12 SrTi2OHoc. Note that there is a possibility that less than When synthesis is performed in the air, europium titanate 5 at. '% of oxygen defects are present in the sample. It was EuTi2O, having a pyrochlore structure is obtained. It was confirmed by the quadrupole mass spectrometry and the found that the same hydrogenation phenomenon occurred thermogravimetric analysis that the oxygen content and the when the same heat treatment conditions were applied, that hydrogen content in the sample that were determined by the is, up to about 20 at. '% of oxygen in oxygen sites was diffraction experiment were correct. FIG. 5 illustrates the substituted with hydrogen. determined crystal structure (right) of the sample after the FIG. 8 illustrates change in the concentration of H gas heat treatment and the crystal structure (left) of the sample detected with a quadrupole mass spectrometer when before the heat treatment. In the Sr., TiO, and Sr TiO, after EuTiO, Ho was heated from room temperature to 600 at the heat treatment, some of oxide ions are substituted with 10 hydride ions. 10/min while an argon gas was caused to flow at a flow rate FIG. 6 illustrates change in the concentration of H gas of 300 mL/min. The EuTiOH has a maximum H gas detected with a quadrupole mass spectrometer when desorption at around 450. Sr TiO, Ho and Sr TiOHo was heated from room INDUSTRIAL APPLICABILITY temperature to 800° C. at 10°C/min while an argon gas was 15 caused to flow at a flow rate of 300 mL/min. For compari The present invention provides a novel hydride ion/ son, SrTiO2, Ho having a perovskite structure was also electron mixed conductor composed of a perovskite oxide measured under the same conditions. FIG. 6 also shows the containing titanium, which is an abundant element. The data. SrTiO2.7Ho has a maximum H gas desorption at hydride ion/electron mixed conductor is promising as a around 400° C. whereas SrTi2OHo has a maximum H mixed ion conductor composed of a ceramic material having gas desorption at around 480° C. and Sr., TiOH has a characteristics that have not been realized in known oxide maximum H gas desorption at around 620° C. This result ion conductors. The Ti-containing perovskite oxide-hydride shows that, in an inert atmosphere, strontium titanate having of the present invention can also be used as a hydrogen a layered structure can be stably present as an oxide-hydride absorption/desorption material. at high temperatures compared with the perovskite strontium 25 titanate. The invention claimed is: 1. A mixed conductor having hydride ion conductivity and EXAMPLE 4 electron conductivity, comprising perovskite oxide having Europium titanate (EuTiO) particles having a perovskite 30 hydride ion conductivity, wherein 1 at. '% or more of oxide Structure and synthesized by a complex polymerization ions contained in a titanium-containing perovskite oxide are substituted with hydride ions (H). method (citric acid method) in a reducing atmosphere were 2. A method for manufacturing a powder of the mixed fired and then stored in a glove box to prevent the adhesion conductor according to claim 1, the method comprising: of moisture in the air. Three equivalents of Cah powder and preparing a titanium-containing perovskite oxide powder the EuTiO, particles were mixed with each other in a glove 35 box and molded into a pellet using a hand press. The pellet as a starting material; and was inserted into a Pyrex (registered trademark) tube having keeping the titanium-containing perovskite oxide powder an internal volume of about 15 cm and vacuum-sealed. together with a powder of an alkali metal or alkaline earth metal hydride selected from lithium hydride Three samples were heat-treated at a reaction temperature of (LiH), calcium hydride (CaH), strontium hydride 550, 575, and 600, respectively, for 48 hours to cause a 40 (Srh2), and barium hydride (BaH) in a temperature hydrogenation reaction. The samples after the heat treatment range of 300° C. or higher and lower than a melting were treated with a 0.1 M NHCl methanol solution to point of the hydride in a vacuum or an inert gas remove an unreacted CaF2 and a by-product CaO that were atmosphere to substitute some of oxide ions in the attached to a product. oxide with hydride ions. The color of the EuTiO, before the hydrogenation reac 45 3. A method for manufacturing a thin film of the mixed tion was black, and the color of the samples washed with a conductor according to claim 1, the method comprising: 0.1 M NHCl methanol solution was also black. There was preparing a titanium-containing perovskite oxide thin film no difference in color in terms of reduction temperature. The as a starting material; and obtained samples were found to maintain a perovskite keeping the titanium-containing perovskite oxide thin crystal structure from powder X-ray diffraction. The sample 50 film together with a powder of an alkali metal or before the heat treatment and the samples after the heat alkaline-earth metal hydride selected from lithium treatment had only a cubic crystal structure at room tem hydride (LiH), calcium hydride (CaFI), strontium perature. hydride (SrH), and barium hydride (BaFI) in a tem It was confirmed by Rietveld analysis of a radiation X-ray perature range of 300° C. or higher and lower than a diffraction pattern that a sample obtained by hydrogenating 55 europium titanate having a pyrochlore structure described melting point of the hydride in a vacuum or an inert gas below had a cubic perovskite structure and a composition of atmosphere to substitute some of oxide ions in the EuTiO, Ho. It was confirmed by the quadrupole mass oxide with hydride ions. spectrometry and the thermogravimetric analysis that the 4. A hydrogen electrode, a hydrogen permeation mem oxygen content and the hydrogen content in the sample that 60 brane, or a hydrogen gas sensor using the mixed conductor were determined by the diffraction experiment were correct. according to claim 1. FIG. 7 illustrates the determined crystal structure (right) of 5. A hydrogenation catalyst using the mixed conductor the sample after the heat treatment and the crystal structure according to claim 1. (left) of the sample before the heat treatment. In the EuTiO, 6. A hydrogen absorption/desorption material using the after the heat treatment, some of oxide ions are substituted mixed conductor according to claim 1. with hydride ions.