Crystalline compound and method for producing crystalline compound

Abstract

This crystalline compound has the compositional formula SrXAlOy, and contains strontium, aluminum, and oxygen. In the compositional formula, x and y are variables. In the compositional formula, the value of x is in the range of 1.6-2.1. In the compositional formula, the value of y is in the range of 3.1-4.1.

Description

Crystalline compound and method for producing the same

[0001] The present disclosure relates to crystalline compounds and methods for making crystalline compounds.

[0002] With climate change and resource depletion accelerating, there is a strong demand for sustainable energy conversion and environmentally friendly chemical reactions. Specifically, the development of catalytic materials with reduced reliance on rare metals, efficient hydrogen generation without or with reduced rare metals, and catalytic materials capable of environmentally friendly chemical reactions are anticipated. Furthermore, for applications in electronic devices, the discovery of materials that retain magnetism at high temperatures and exhibit novel luminescence properties is required. Materials that maintain ferromagnetism at high temperatures, i.e., have high Curie temperatures, can be used in energy conversion and catalytic materials. Ferromagnetism typically requires partially occupied d or p orbitals, resulting in uncancelled electron spin moments. Non-Patent Documents 1 and 2 document the unexpected discovery of ferromagnetism in the diluted magnetic semiconductor (In,Mn)As. Subsequently, the theoretical prediction of room-temperature ferromagnetism in ZnO, presented in Non-Patent Document 3, accelerated research on this topic. Unexpected ferromagnetism has also been observed in HfO2 thin films without doping with magnetic impurities (Non-Patent Document 4) and in other defective oxides, interface structures, and nanocomposites (Non-Patent Documents 5 and 6).

[0003] H.Ohno, H.Munekata, T.Penney, S.von Molnar, L.L.Chang, Magnetotransport properties of p-type (In,Mn)As diluted magnetic III-V semiconductors. Phys. Rev. Lett. 68, 2664-67(1992). doi:10.1103 / PhysRevLett.68.2664H. Ohno, Making nonmagnetic semiconductor ferromagnetic. Science 281, 951-956 (1998).doi:10.1126 / science.281.5379.951.T. Dietl, H. Ohno, F. Matsukura, J. Cibert, D. Ferrand, Zener model description of ferromagnetism in zinc-blende magnetic semiconductors. Science 287, 1019-22 (2000). doi: 10.1126 / science.287.5455.1019M. Venkatesan, C. Fitzgerald, J. M. D. Coey, Thin films: unexpected magnetism in a dielectric oxide. Nature 430, 630 (2004). doi: 10.1038 / 430630aJ. M. D Coey, d0 30 ferromagnetism. Solid State Sciences 7, 660-667 (2005). doi:10.1016 / j.solidstatesciences.2004.11.012Tomasz Dietl, A ten-year perspective on dilute magnetic semiconductors and oxides, Nature Materials 9, 965-974 (2010). doi: 10.1038 / nmat 2898.

[0004] Materials used in energy conversion or as catalysts must sometimes maintain ferromagnetism during the energy conversion process or chemical reaction. If the energy conversion process or chemical reaction is performed at high temperatures, the Curie temperature of the material must be high. Currently, materials used in energy conversion or as catalysts tend to rely on rare metals. Therefore, there is a need for crystalline compounds with high Curie points that reduce dependence on rare metals, and for methods of manufacturing such crystalline compounds.

[0005] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a crystalline compound having a high Curie point that can be used, for example, in energy conversion or as a catalyst, and a method for producing the crystalline compound.

[0006] The crystalline compound according to the present invention has the composition formula Sr Ｘ AlO ｙ where x is between 1.6 and 2.1, and y is between 3.1 and 4.1. This crystalline compound has ferromagnetism due to the p orbital, and maintains its magnetism even in a high-temperature environment of 900K. This makes it possible to design new materials that are independent of or have reduced dependence on rare metals for energy conversion, catalysis, and other applications.

[0007] The method for producing a crystalline compound according to the present invention is characterized in that a pellet obtained by pressing a powder containing aluminum hydroxide or aluminum oxide and europium oxide and a strontium (Sr) compound are heated to 1300 to 1900°C in a reducing atmosphere and then slowly cooled. ２ AlO ４ In this study, fibrous Sr ２ AlO ４ was obtained.

[0008] Other features of the present invention will become apparent below.

[0009] A crystalline compound with a high Curie point and a method for producing the crystalline compound can be provided. A p-orbital ferromagnet resulting from under-bonded oxygen can be obtained. Furthermore, the crystalline compound exhibits high-intensity elastic mechanoluminescence that can be seen with the naked eye, a feature not found in other mechanoluminescent materials. Such high-intensity luminescence properties enable visualization of stress distribution in industrial and engineering fields.

[0010] 1 is an image of a crystalline compound according to the present embodiment. ２ AlO ４ 1 shows the structural characteristics of Sr. 2 shows the results of an X-ray diffraction experiment. ２ AlO ４ 1 is a table showing the structural characteristics of the present invention; 2 is a table showing the bond lengths between oxygen O and the surrounding Sr and Al; 3 is a graph showing the bond lengths between oxygen O and the surrounding Sr and Al; and 4 is a diagram explaining the structural change; and 5 is a table showing the bond lengths between oxygen O and the surrounding Sr and Al at 75°C. ２ AlO ４ 1 is a table showing the structural characteristics of Sr ２ AlO ４ 1 shows the analysis results of the magnetism of Sr. ２ AlO ４ 1 is a diagram showing experimental results of the electrical characteristics of Sr 2.25, and a diagram showing calculation results of the density of states of Sr 2.15 obtained by theoretical calculation. ２ AlO ４ 1 shows the electronic structure of Sr ２ AlO ４FIG. 1 is a diagram showing a simplified model for investigating magnetic coupling in a sample; FIG. 2 is a diagram showing the intensity of elastic mechanoluminescence; FIG. 3 is a photograph of each sample after firing; FIG. 4 is a photograph of a sample irradiated with ultraviolet light; FIG. 5 is a photograph of a sample before and after firing; FIG. 6 is a photograph of a sample irradiated with ultraviolet light; FIG. 7 is a diagram showing the dependence of fiber recovery amount on Eu composition; FIG. 8 is a diagram showing an example where the substitution ion is changed from Eu to Gd; FIG. 9 is a diagram showing an example where the substitution ion is changed from Eu to Nd; FIG. 10 is a diagram showing an example where the substitution ion is changed from Eu to Sm; FIG. 11 is a diagram showing an example of a sample where the raw material arrangement pattern is changed; FIG. 12 is a flowchart showing a method for producing a crystalline compound according to a comparative example; FIG. 13 is a diagram showing an example of hand mixing and ball milling; FIG. 14 is a diagram showing the results of X-ray diffraction measurement; FIG. 15 is a photograph of a sample irradiated with ultraviolet light; FIG. 16 is a diagram showing the results of X-ray diffraction measurement.

[0011] The inventors have been exploring ferromagnetism in mechanoluminescent materials that can excite strong luminescence by mechanical stimulation within the elastic deformation range. ２ O ４ The inventors have found that SrAl becomes ferromagnetic at temperatures below 5 K. ２ O ４ The inventors have found that the fibrous crystals grown on the surface of ceramic pellets have a Curie temperature Tc much higher than room temperature. The inventors have made extensive research into the cause of this extraordinary Curie temperature Tc, which cannot be explained by a small amount of magnetic impurities or oxygen defects, and have found that the above-mentioned fibrous crystals are a novel crystalline compound Sr with an unreported crystal structure. ２ AlO ４ Furthermore, it was confirmed that Sr ２ AlO ４ Experimental results combined with theoretical calculations for ferromagnetism have shown that the exceptional Curie temperature, Tc, is an intrinsic effect of the p-orbitals of oxygen ions in this compound. This is the intrinsic ferromagnetism of p-orbitals.

[0012] <Crystalline Structure and Characteristics> Figure 1 shows images of the crystalline compound according to this embodiment. Figure 1A shows the single crystal material Sr ２ AlO４ 1B is a microscopic image of the single crystal material. The single crystal material grew preferentially along the

[110] crystal direction. According to one example, the crystalline compound according to the present invention is a fibrous single crystal semiconductor. FIG. 1B shows a fibrous multi-layer Sr ２ AlO ４ 10 is a graph showing the light emission by irradiating UV light of λ=365 nm onto the

[0013] FIG. 2A shows a single crystal Sr ２ AlO ４ 3 shows an example of an X-ray diffraction pattern using synchrotron radiation for single crystal Sr. From the X-ray diffraction spots using synchrotron radiation, it can be seen that the fibrous crystal is a single crystal. ２ AlO ４ This figure details the X-ray diffraction of SiO2 using synchrotron radiation. The upper panel of Figure 3 shows the experimental setup at 30°C and 75°C, with diffraction spot indices labeled. The images in this upper panel reveal structural changes. The bottom three columns of Figure 3 show the diffraction patterns in the reciprocal lattice. The top three patterns, the middle three patterns, and the bottom three patterns are those viewed along the a-axis, b-axis, and c-axis, respectively. The left pattern was obtained at 30°C, the center pattern at 50°C, and the right pattern at 75°C. The structures above 75°C are paired by inversion, i.e., merohedral twins (-100,0-10,00-1).

[0014] From the X-ray diffraction pattern in Figure 3, the aforementioned fibrous crystals are the new material Sr ２ AlO ４ It was found that the structure was the same as that shown in Figure 2B. Figure 2B shows the structure of the novel material Sr at 30°C. ２ AlO ４ 2B shows the structure of the compound. In FIG. 2B, the white wedges at the Sr and O4 sites represent vacancies. The Sr site of this crystalline compound contains an Eu ion. FIG. 2B also shows that O4 has one less bond to Sr than O1, O2, and O3.

[0015] Figure 4 shows the new material Sr at 30°C. ２ AlO ４ This table shows detailed information about the structure of Sr. A small amount of Eu ions, about 0.8 atomic percentage (about 0.4 atomic percentage in total, hereafter referred to as "atomic percentage"), is preferentially placed in the Sr2 site. On the other hand, as shown in Figure 4, there are 3.4 atomic percentage oxygen vacancies in the O4 site. Thus, Sr ２ AlO ４ Each O site in the structure contains a few percent of oxygen vacancies.

[0016] Figure 5 shows the Sr ２ AlO ４ This table shows the bond lengths of oxygen O and the surrounding Sr and Al in the SiO2 structure. It is clear that O4 is underbonded. That is, O4 has a very short bond length of 2.3964(6) Å with the nearest neighbor Sr2, which is Eu-doped (see Figures 5 and 6).

[0017] Figure 6 shows the Sr ２ AlO ４ This figure shows the bond lengths between oxygen O and the surrounding Sr and Al atoms in the structure. Focusing on O4, O4 has one less bond with Sr, resulting in an insufficient bond. In other words, the distance between the nearest Sr atom and O4 is 3.3850(7) Å, which is longer than the other O-Sr atomic distances.

[0018] As can be seen from Figures 2B, 6, and 5, the O4 atom is under-bonded by bonding to one Al and three Sr (i.e., two Sr1 and one Sr2), while all the O ions at other sites are bonded to one Al and four Sr (i.e., two Sr1 and two Sr2). ２ AlO ４ One O site in the compound is bonded to one Al and three Sr atoms, and Sr ２ AlO ４The O sites other than the one O site included in are bonded to one Al and four Sr. According to one example, the four O sites in this crystalline compound can be said to consist of: a first O site bonded to one Al and bonded to a first Sr group of four Sr; a second O site bonded to one Al and bonded to a second Sr group of four Sr; a third O site bonded to one Al and bonded to a third Sr group of four Sr; and a fourth O site bonded to one Al, bonded to a fourth Sr group of three Sr, and bonded to a remote Sr of one Sr. The bond lengths between the first Sr group and the first O site, the bond length between the second Sr group and the second O site, the bond length between the third Sr group and the third O site, and the bond length between the fourth Sr group and the fourth O site are within predetermined specific ranges. For example, Figure 6 illustrates such a specific range from 2.375 Å to 3.0 Å. However, the bond length between the remote Sr and the quaternary O site is longer than the upper limit of this specific range. Figure 6 illustrates that one Sr bonded to the O site has a bond length of 3.4 Å.

[0019] Such insufficient or low bonding of O4 was also revealed by theoretical calculations. Figures 2C and 2D show the results of such theoretical calculations. Figures 2C and 2D show the electron density distribution calculated by the DFT+U method (U=12.0). DFT will be described later. Figures 2C and 2D show the electron density contour maps calculated for the two crystal planes identified in Figure 2B, respectively. Figures 2C and 2D show the main structural features of the O2 and O4 atoms. Figure 2D shows the structure of a normal O 2－ The number of Sr cations bonded to the O atom is one less than that of the O atom in the state － The figure shows O4 ions in the α-state. The number of Sr atoms bonded to O2 and O4 on each crystal plane is 3 and 2, respectively, but there is one Sr and one Al atom in the direction almost perpendicular to each plane in both O2 and O4. The detailed bond lengths are shown in Figures 5 and 6.

[0020] FIG. ２ AlO ４ 1 is a diagram for explaining the structural change of Sr ２ AlO４ The structure of ZnO changes from monoclinic to orthorhombic between 50 and 75°C. This structural change can be directly understood from the change in the diffraction spots in Figure 3. Figure 7A is a crystal structure model showing the high-temperature phase of the orthorhombic system at 75°C. Figure 7B shows the temperature dependence of the unit cell parameters. The change in the unit cell parameters is accompanied by the substitutions a → c, b × 3 → a, and c → b between 50 and 75°C, indicating the structural change from monoclinic to orthorhombic. The values ​​of the unit cell parameters are unified by their respective values ​​at 30°C.

[0021] Figure 7A shows that the high temperature phase has 12 O sites, of which O4, O8, and O12 are poorly bonded due to one less bond to Sr. This is summarized in more detail in the table in Figure 8. Figure 8 shows the Sr at 75°C. ２ AlO ４ This is a table showing the bond lengths between oxygen O and the surrounding Sr and Al for the above. From this table, we can see that O4, O8, and O12 have one less bond with Sr, resulting in an insufficient bond.

[0022] Figure 9 shows the Sr ２ AlO ４ This figure shows the structural information for . As mentioned above, the structural change from monoclinic to orthorhombic occurs with the a → c, b × 3 → a, and c → b substitutions. From this figure, it can be seen that a significant amount of oxygen vacancies are generated at the O4, O8, and O12 sites.

[0023] <Magnetic> Chemical formula is Sr ２ AlO ４ In the case of Sr, the usual oxygen valence is not observed. ２＋ and Al ３＋ The ionic state of Sr is considered stable, and the electron orbital [Kr]5s ２ and the electron orbital [Ne]3s in Al ２ 3p １ When evaluated from － The unusual partial occupation of the p-orbitals of the ions is expected, which may qualitatively correspond well to the surroundings of O4 in the room temperature phase or O4, O8, and O12 in the high temperature phases. Indeed, this new compound is characterized by the presence of Sr２ AlO ４ 1.0 μ per molecule Ｂ This shows ferromagnetism with a saturation magnetization of -2, justifying this prediction. Conventionally, the stable valence of oxygen ions was -2, but as mentioned above, we have created a -1 valence. Conventional technology only has minute p-orbital ferromagnetism caused by impurity bands, but as mentioned above, we have realized full-scale p-orbital ferromagnetism. The design concept of stable monovalent oxygen ions provides new guidelines for the design of new materials that can create new luminescent materials, catalytic effects, energy materials, and other unknown functional properties. Incidentally, the valence of oxygen is a determining factor in the properties of oxides, but the outermost electron orbital of oxygen is 2s. ２ 2p ４ (2 electrons in the 2s orbital, 4 electrons in the 2p orbital), so the valence that can usually exist stably is -2 O (to capture 2 electrons from the cation to form a stable closed shell of 8 electrons) 2－ On the other hand, in the lithium ion battery material LiCoO2 and TiO2 that can decompose water into hydrogen when irradiated with ultraviolet light, oxygen can deviate from the stable divalent state of -2 in an unstable non-equilibrium state, which has a great effect on energy conversion and catalytic effects. ２ AlO ４ It was found that the new material Sr exhibits a stable monovalent oxygen ion state and p-orbital ferromagnetism. ２ AlO ４ is a stable negative monovalent O － It was found that this substance achieves the oxygen state. 2－ So 2s ２ 2p ６ As the electron orbital moves up and down, the magnetism disappears. － In this state, ２ 2p ５ Therefore, it was found that the p orbital with an unpaired electron creates ferromagnetism. Materials with such properties will not only exhibit new mechanoluminescence and ferromagnetism, but will also provide new guidelines for the design and creation of new oxides, and are expected to be particularly effective in energy conversion and catalytic effects.

[0024] FIG. 10 shows the Sr ２ AlO ４FIG. 10A shows the ferromagnetism of Sr ２ AlO ４ Figure 10B shows the magnetization vs. magnetic field characteristics of Sr-Al-O oxide from 2 K to 400 K. This characteristic curve has a small hysteresis similar to that of ZnO. Figure 10B shows the saturation magnetic moment and the temperature dependence of the magnetic moment measured at H = 30 kOe. In the figure, the magnetic moment is represented by a series of connected plots, and the saturation magnetic moment is represented by 12 slightly larger circles. The large increase in the low-temperature range in Figure 10B is likely due to the magnetic moment induced by oxygen vacancies, as this has been universally observed in Sr-Al-O oxides. Figure 10C shows the magnetic susceptibility χ up to 1000 K in heated and cooled environments. Figure 10D shows the ferromagnetic M-H characteristics at 800 K.

[0025] Crystal compound Sr ２ AlO ４ The Curie temperature Tc of ZnO reaches approximately 900 K. Theoretical calculations predict that there is no change in magnetic properties accompanying the structural change from monoclinic to orthorhombic. This will be discussed later.

[0026] Additional experiments using an atomic-scale magnetic probe for muon spin rotation / relaxation (μSR) spectroscopy revealed the presence of a static internal field, i.e., bulk ferromagnetism throughout the sample.

[0027] FIG. 11 shows the results of the experiment using approximately 400 mg of Sr ２ AlO ４ Figure 11 shows the μSR asymmetry spectra for the assembly. Figure 11A shows the zero-field μSR asymmetry spectra at 304 K, 202 K, and 101 K. It can be seen from Figure 11A that the lower the temperature, the stronger the internal magnetic field. Figure 11B shows the longitudinal magnetic field asymmetry spectrum, which explains the static nature of the internal magnetic field. Detailed measurements have shown that a fraction of the injected muons are μ ＋ +e －It turns out that the muonium atom forms with an electron, like Mu. Therefore, a precise determination of the μ / Mu ratio would be required for quantitative analysis. Since the paramagnetic state cannot be measured in this case (the muon's mass is about one-ninth that of a proton, so it hops around quickly in the material, and therefore the μSR technique cannot be applied at elevated temperatures), a quantitative analysis of the internal local magnetic field is not possible.

[0028] As shown in Figure 11, a strong muon spin polarization is observed at low temperatures, suggesting that the internal magnetic field becomes gradually stronger with decreasing temperature. On the other hand, the muon spin polarization separated by the external longitudinal magnetic field clearly indicates the static nature of the internal magnetic field, i.e., magnetic order.

[0029] Electrical properties and p-orbital ferromagnetism Experimentally observed electrical properties and orbital states of oxygen. Figure 12 shows experimentally observed Sr ２ AlO ４ 12A shows the electrical properties of a single crystal Sr ２ AlO ４ The electrical conductivity along the

[110] crystallographic direction of the fiber is shown. ２ AlO ４ is the band gap ε ｇ The band gap of ~1.13 (±0.25) eV corresponds to the intrinsic band gap, as described below.

[0030] The speculation of partially occupied p-orbitals was directly substantiated by synchrotron X-ray absorption spectroscopy (XAS) analysis performed in bulk-sensitive fluorescence mode. Figure 12B shows the X-ray absorption spectra of Sr at 300 K. ２ AlO ４Figure 12B shows the oxygen 1s X-ray absorption edge in SiO2. In Figure 12B, two additional pre-absorptions centered at E = 532.4 eV and 533.6 eV were observed before the main absorption peak at 534.9 eV. The dashed line represents the normal absorption curve, which aids in understanding the pre-absorptions. The complex fluctuations above 536 eV are due to the various contributions of Al and Sr. XAS of the O K-edge absorption measures absorption from the oxygen 1s orbital to unoccupied orbitals, and two additional pre-absorptions with peaks at E = 532.4 eV and 533.6 eV, or 2.5 eV and 1.3 eV, respectively, lower than the main absorption peak at 534.9 eV. These two additional pre-absorptions clearly indicate the unique unoccupied oxygen states in this crystal.

[0031] Theoretically calculated electrical properties Density Functional Theory (DFT) provides powerful predictions and proofs for both the crystal structure and electronic structure. ２ AlO ４ 13A and 13B show the calculated densities of states for the monoclinic and orthorhombic crystal structures, respectively. ２ AlO ４ The DFT calculations show that the asymmetric density of states for the electron spin-up and spin-down is ~1μ Ｂ / Sr ２ AlO ４We predicted that this would result in a ferromagnetic moment of 1.0. However, the metallic band structure features are inconsistent with those of semiconductors. As illustrated by numerous studies in various materials, particularly transition metal oxides, the Hubbard U correction (DFT+U) must be used to overcome the limitations of standard DFT for strongly correlated systems, taking into account in situ Coulomb interactions. Our DFT+U calculations showed that U = 12.0 is closest to the experimentally observed lattice constant for a monoclinic structure. Furthermore, the density of states (DOS) calculated under this condition is in consistent agreement with the experimentally observed electronic properties.

[0032] FIG. 14 shows the composition formula Sr ２ AlO ４ 14A shows the theoretical calculation results for the electronic structure of monoclinic Sr ２ AlO ４ As shown in Figure 14A, an asymmetric overall density of states band with uncancelled ↑ and ↓ spins is obtained, which explains the observed ferromagnetism. B per Sr ２ AlO ４ and E Ｆ The occupied bands of uncanceled spin-up and spin-down electrons lower than EE explain the experimentally observed ferromagnetism. F For the major unoccupied band at >3.82 eV, EE F Two unoccupied O 2p bands centered at = 1.26 eV and 2.52 eV show good agreement with the experimental results in Fig. 12. Most of the uncanceled magnetic moment is attributed to the O 2p orbitals. The DOS of the partial orbital waves indicates that most of the ferromagnetic moment is attributed to the O 2p orbitals with a minor contribution from the Sr 4d electrons.

[0033] Figure 14B shows that the DOS of the O 2p orbital is decomposed into the local DOS of the oxygen atoms, indicating that the uncanceled spin and unoccupied O 2p bands arise primarily from the O4 site. Further decomposition of the O 2p orbital into the local DOS of the O1-O4 atoms shows that the O4-2p orbital electrons provide the dominant contribution (Figure 14B), which is in good agreement with the structural features shown in Figure 2. In particular, the EE F = 1.26 eV and 2.52 eV, i.e., two unoccupied O4-2p minute bands at 2.56 eV and 1.30 eV, respectively, are F The fact that the band gap is >3.82 eV below the main unoccupied band is in good agreement with the pre-absorption peaks in the XAS data in Figure 12B. In the latter case, their values ​​are 2.5 eV and 1.3 eV, respectively, below the main absorption peak. Also, the calculated band gap is 1.26 eV, which is in line with the measured band gap ε in Figure 12A, taking into account the experimental error. g =1.13 (±0.25).

[0034] The inventors calculated the material SrAlO ３ It was confirmed that the theoretically predicted ferromagnetism was observed. ３ Although O did not have the structural features that bind oxygen poorly, it should have a similar normal oxygen value, i.e., O － The state can be assumed.

[0035] Sr ２ AlO ４ It has been found that the high transition temperature ferromagnetism in Sr is mainly caused by the uncancelled spin of the oxygen p-orbital electrons. ２ AlO ４ This material behaves as a ferromagnetic material due to the action of the p orbital of the O ions in the material. This is the first time that a p orbital type ferromagnetic material has been discovered.

[0036] FIG. 15 shows the Sr ２ AlO ４Figure 15 shows a simplified model for investigating magnetic coupling in ZnO. In Figure 15, well-bonded O atoms are omitted. Figure 15A shows the monoclinic structure at room temperature, omitting well-bonded O atoms. In the 30°C monoclinic structure, O4, which plays an important role in ferromagnetism, has short O4-O4 chain distances of 2.9436 Å and 3.3600 Å along the zigzag chains. In comparison, the O-O distance in ZnO is about 3.26-3.29 Å. Therefore, strong magnetic interactions are expected between O4-O4 chains. The defective Sr / Eu sites have spins, which interact with the Sr and oxygen vacancies and the Eu. ２＋ The inventors predict that three-dimensional ferromagnetic long-range order can be efficiently constructed from the magnetic coupling between the Sr2 chains due to the Sr / Eu spins. The distance between the Sr2 and the nearest O4 is short at 2.3955 Å, and the distance between the O4 and the neighboring chain is 3.6360 Å.

[0037] FIG. 15B shows orthorhombic Sr ２ AlO ４ This diagram shows only the under-bonded oxygen atoms at the O4, O8, and O12 sites in the O4-O12 and O8-O8 chains. In the orthorhombic structure, the three-dimensional coupling of the O4-O12 and O8-O8 spins can be easily derived from the Sr / Eu spins. The O8-Sr3 distance is 3.679 Å, and the O4-Sr6 distance is 3.640 Å. As is known for oxides, magnetic polarons with typical spacings greater than 10 Å have been theoretically proposed to explain room-temperature ferromagnetism in oxides such as ZnO. Sr ２ AlO ４ The particularly high Curie temperature Tc in may be explained by extending the theory to include, for example, bound magnetic polarons.

[0038] The concept of p-orbital ferromagnetism, resulting from the coupling of under-bonded oxygen atoms with defects, can be applied to material design, thereby opening new avenues for the creation and engineering of spin electronics. What makes this material even more attractive is the coexistence of mechanically stimulated luminescence (mechanoluminescence: ML) in the elastic deformation region, i.e., elastic mechanoluminescence. Such a property allows visualization of stress distribution, making it promising for industrial and engineering applications. One small Sr ２ AlO ４ The elastic ML from the crystal is visible to the naked eye, which is a high-performance elastic ML material that can be imagined, SrAl with 0.05% strain. ２ O ４ It is 30 times stronger than Sr ２ AlO ４ and SrAl ２ O ４ 16 shows the elastic ML of the two materials normalized by mass. The inset in the upper left of Fig. 16 shows the elastic ML of Sr during elastic ML emission. ２ AlO ４ This is a single-frame image of the fiber (circular frame part).

[0039] As mentioned above, the new oxide semiconductor Sr ２ AlO ４We have discovered intrinsic p-orbital ferromagnetism in ZnSe. This new semiconductor exhibits stable ferromagnetism up to ∼900 K, far exceeding the highest Tc ever recorded in diluted magnetic or defect-containing semiconductors. Furthermore, this material exhibits intriguingly bright elasto-mechanoluminescence, which may enable unprecedented mechano-spin-photonics engineering. The material of the present invention also sheds light on a long-standing and intensely debated new type of ferromagnetism in defect oxides. A promising candidate mechanism is that defects create spin-split impurity bands, which give rise to small ferromagnetic moments in defect oxides. Our experimental results and theoretical calculations support this hypothesis and aid in understanding the highly unusual room-temperature Tc in defect oxides. Orbital physics of anisotropically shaped d-orbital electrons and Coulomb interactions has been studied to explain high-temperature superconductivity and colossal magnetoresistance. This invention demonstrates that various phenomena can be studied by extending orbital physics to p-orbitals.

[0040] <Example of manufacturing method> Eu-doped Sr ２ AlO ４ can be produced, for example, by the following method: First, a powder containing a Sr compound, aluminum hydroxide or aluminum oxide, and europium oxide is pressed to form a pellet. ３ , Al(OH) ３ , Eu ２ O ３ , and H ３ BO ３ The high purity powders are mixed and pressed to form a pellet. The pellet is then heated to 1300-1900°C in a reducing atmosphere and slowly cooled to cause a solid-state reaction, resulting in Eu-doped Sr ２ AlO ４ According to one example, it is heated in an Ar-5% H2 atmosphere for about 4 hours and then slowly cooled. ３ BO ３ The crystalline compounds (e.g., Al) act as a flux and sublimate at high temperatures. ２ O３ The crystals are formed in a fiber shape (towards the periphery of the crucible). The preferred growth direction of this crystalline compound is

[110] .

[0041] Sr having the above characteristics ２ AlO ４ The composition formula has a certain range. For example, x is 1.6 or more and 2.1 or less, and y is 3.1 or more and 4.1 or less. Ｘ AlO ｙ The inventors have found that the sample synthesized with a non-stoichiometric composition is a crystalline compound, and that the crystal structure of the sample is determined by X-ray diffraction (XRD). ２ AlO ４ In other words, the composition range of the crystal was analyzed using EDX, EPMA, and fluorescent X-rays, and it was found that the above non-stoichiometric ratio of Sr ２ AlO ４ The crystalline structure was maintained. This crystalline compound can be said to be a non-stoichiometric compound that has the same crystalline form over a wide composition range. Furthermore, as a result of the composition analysis of the fiber by the inventors, it was found that there was a distribution depending on the location, and this distribution exceeded the range of x being 1.6 or more and 2.1 or less, and y being 3.1 or more and 4.1 or less. In other words, it was found that the above-mentioned crystalline structure was maintained at a composition that exceeded the range of x being 1.6 or more and 2.1 or less, and y being 3.1 or more and 4.1 or less. Therefore, this numerical range is sufficiently narrow, and it is believed that the above-mentioned properties can be obtained with a composition within this numerical range. In terms of stoichiometry, Sr ２ AlO ４ Therefore, the stoichiometric ratio of oxygen for Sr1.6 to 2.1 is 3.2 to 4.2. 2.1 When y is the upper limit of 4.1, oxygen deficiency occurs. 1.6 For example, when y is the lower limit of 3.1, oxygen deficiency occurs. It is thought that the charge balance of the adsorbed oxygen in this crystal allows oxygen deficiency and excess. Here, x is 1.6 to 2.1, and y is 3.1 to 4.1. However, in another example, x can be 1.9 to 2.1, and y can be 3.7 to 4.1.

[0042] <Consideration of materials to replace part or all of Sr> Sr ２ AlO ４ We investigated whether part or all of the Sr in the Sr could be replaced with Ba ions. １－ｙ ,Ba ｙ ) ２ AlO ４ Three samples were prepared in which the value of y was changed to 0, 0.1, and 1 in 0.5 at% Eu. In other words, three samples with the following compositions were prepared: Sample with y = 0: Sr ２ AlO ４ : 0.5 at% Eu y = 0.1 sample: (Sr ０．９ ,Ba ０．１ ) ２ AlO ４ : 0.5 at% Eu Sample with y = 1: Ba ２ AlO ４ : 0.5% at Eu The three samples were manufactured in the same manner as the above-mentioned manufacturing method, that is, by forming pellets, heating, and slow cooling, except for the presence or absence of Ba ion substitution. Figure 17 shows photographs of each sample after firing. The upper row of Figure 17 is a photograph of the lid of the firing vessel, and the lower row is a photograph of the firing vessel body and pellet. When fibers grow in the pellet, fibers also grow on the lid of the firing vessel, turning the lid black. When observing the three lids in the upper row of Figure 17, the lid on the left, which contains only Sr and does not contain Ba ions, is black, so it is clear that Sr ２ AlO ４ The central lid, which is made of Ba and Sr at a ratio of 1:9, is slightly black (Sr ０．９ ,Ba ０．１ ) ２ AlO ４ The right cover, which contains only Ba and does not contain Sr, is not blackened, so Ba ２ AlO ４ Therefore, it was found that although the yield decreased as the Ba content increased, crystal formation itself was possible even with Ba / Sr=1:9.

[0043] Figure 18 shows photographs of these three samples irradiated with ultraviolet light. The upper row shows photographs when 254 nm ultraviolet light was applied, and the lower row shows photographs when 365 nm ultraviolet light was applied. In each photograph, the lid of the firing vessel is at the top right, and the main body of the firing vessel and pellets are at the bottom left. In the cases of Ba / Sr = 0:1 and Ba / Sr = 1:9, as shown by the arrows, the Sr ２ AlO ４ Crystal and (Sr ０．９ ,Ba ０．１ ) ２ AlO ４ The luminescence of each crystal was confirmed.

[0044] Since fiber-shaped crystal growth is possible even when a portion of Sr is replaced with Ba ions, it is believed that fiber-shaped crystal growth is also possible when a portion of Sr is replaced with ions of Ca or Mg, which are Group 2 elements like Sr and Ba. It is possible to replace a portion of Sr with one or more ions of Ba, Ca, or Mg. Theoretically, it is believed that Sr can be completely replaced with Ba, Ca, or Mg, which are also alkaline earth metals. In other words, 0 to 100% of Sr can be replaced with Ba, Ca, or Mg ions. Therefore, fibers can be synthesized using Ba, Ca, or Mg instead of Sr. In the aforementioned experiment, partial replacement of Sr was successful.

[0045] <Dependence on Eu Amount> Next, the influence of the amount of Eu added on the produced crystal was investigated. ２ AlO ４ : xEu, that is, Sr ２ AlO ４Five samples were produced using crystals containing Eu ions, with x values ​​of 0.1%, 0.5%, 1.0%, 1.5%, and 2.5% (% is atomic percentage). The production method was the same as the example of the production method described above, involving pellet formation, heating, and slow cooling. These five samples can be said to be samples with varying amounts of Eu ions substituted for a portion of the Sr. Figure 19 shows photographs of these five samples before and after firing. Figure 19A shows a photograph before firing. Figure 19B shows a photograph after firing. Figure 19B shows that for Eu ion substitution levels between 0.1% and 1.5%, fiber growth led to fiber growth on the lid of the firing container, turning the lid black. When the Eu ion substitution level was 2.5%, no black areas were observed on the lid. This indicates that excessive Eu ion substitution reduces yield.

[0046] Figure 20 is a photograph showing the state of these five samples after ultraviolet irradiation. Photographs are shown for when 254 nm ultraviolet light was applied and when 365 nm ultraviolet light was applied. The lid of the firing container is on the right side of each photograph, and the main body of the firing container and pellets are on the left side. It was confirmed that the luminescence intensity tends to increase as the amount of Eu ions increases. It was found that the fiber yield increases with increasing Eu ion substitution amount up to 1.5%. When the Eu ion substitution amount was 2.5%, as mentioned above, no fiber grew on the lid, but it was confirmed that the lid emitted light.

[0047] Figure 21 shows the dependence of fiber recovery yield on Eu composition. Figures 21A and 21B show that the amount of fiber produced is affected by the amount of Eu ions substituted. This suggests that Eu may play a catalytic role in the fiber growth process.

[0048] <Consideration of Additions Other Than Eu> Up to this point, we have shown an example in which a portion of the Sr ions are replaced with Eu ions. However, a portion of the Sr ions can also be replaced with ions other than Eu ions. Specifically, a portion of the Sr ions can be replaced with at least one of the following elements: La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Cr, Mn, Fe, Co, Ni, and Cu. In other words, the Sr sites can be partially replaced with La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Cr, Mn, Fe, Co, Ni, or Cu ions. According to one example, 0.01 to 10% of the Sr sites can be replaced with these ions. Figure 22 shows an example in which the replacement ion is replaced from Eu to Gd. The manufacturing method is the same as the above-mentioned manufacturing method, involving pellet formation, heating, and slow cooling. Figure 22A shows the pellet placed in a crucible and its configuration before firing. Figure 22B is a photograph of a calcined sample irradiated with 254 nm UV light. Figure 22C is a photograph of a calcined sample irradiated with 365 nm UV light. In both Figures 22B and 22C, the crucible body (the calcination vessel) and pellet are on the left, and the lid is on the right. In Figure 22B, fibers emitting blue light were observed in the pellet. In both Figures 22B and 22C, the lid was non-luminescent, but the inventors confirmed that a larger amount of crystals grew than when Eu was used for the lid. When Gd ions were substituted, crystals that emitted no visible UV light but emitted near-infrared light were obtained in higher yields than when Eu was used. On the lid side, the energy of the photons emitted by the electronic transition of Gd ions is in the near-infrared range, so they were not captured with a visible light camera. As mentioned above, the light emitted from the lid side is near-infrared, unlike visible light. This material is also highly magnetic, making it useful. On the other hand, it is believed that a different crystalline phase is formed on the pellet side. Figure 23 shows an example in which the substitution ion was changed from Eu to Nd. The manufacturing method is the same as the example of the manufacturing method described above, which involves pellet formation, heating, and slow cooling. Figure 23 shows a photograph of the sample after firing when exposed to 254 nm ultraviolet light.Figure 23 shows a photograph of the crucible body and pellets used as the firing vessel on the left side, and a photograph of the lid on the right. Blue-emitting fibers were observed in the pellet. The lid did not emit visible light under UV light, but near-infrared light was observed. It was confirmed that a larger amount of crystals grew than when Eu was used for the lid. Substitution with Nd ions resulted in crystals that emitted near-infrared light but no visible light under UV light, with a higher yield than when Eu was used. It is believed that the same phenomenon as with Gd ions occurs when Nd ions are used. Figure 24 shows an example in which the substitution ion was changed from Eu to Sm. The manufacturing method is the same as the above-mentioned manufacturing method, involving pellet formation, heating, and slow cooling. Figure 24 shows a photograph of a fired sample exposed to 254 nm UV light. Figure 24 shows a photograph of the crucible body and pellets used as the firing vessel on the left side, and a photograph of the lid on the right side. Light-emitting fibers were observed in the pellet. The lid did not emit visible light under UV light, but near-infrared light was observed. It was confirmed that a larger amount of crystals grew than when Eu was used for the lid. Therefore, when Sm ions are substituted, crystals that do not emit light under ultraviolet light can be obtained in higher yields than when Eu is used. In one example, the oxide semiconductor Sr. ２ AlO ４ The emission wavelength of this oxide semiconductor can be adjusted by selecting Eu, Gd, Nd, or Sm ions to substitute for a portion of the Sr site. Eu and Sm can be primarily used when emitting light in the visible range, while Gd and Nd can be primarily used when emitting light in the near-infrared range. Furthermore, when this oxide semiconductor is considered as a catalyst material, the ability to freely substitute Eu, Gd, Nd, Sm, etc. makes it possible to control the chemical reaction process and induce any other reaction. Elements other than Eu, Gd, Nd, and Sm, as well as Eu, Gd, Nd, and Sm, have emission levels in the visible and near-infrared ranges, and can therefore be used depending on the application. These ions have f and d electron orbitals, which are believed to exhibit diverse electronic, optical, and magnetic properties, as well as to be advantageous in dramatically improving functionality.

[0049] <Study on Pellet Arrangement> The effect of the arrangement of raw materials in the crucible on crystal growth was investigated. Figure 25 shows photographs of four samples with different raw material arrangement patterns, taken after firing by pellet formation, heating, and slow cooling, as in the example of the manufacturing method described above. From the left, the photographs show samples with an arrangement in which Sr powder is provided in the center of the firing container, an arrangement in which Sr powder is spread throughout the firing container, a three-layer structure, and a two-layer structure. A photograph taken from the front of the three-layer structure has been added. In all four samples, the white disk-shaped pellets contain aluminum hydroxide or aluminum oxide and europium oxide. The three-layer structure consists of two white disk-shaped pellets sandwiching a Sr compound pellet. The two-layer structure consists of a Sr compound pellet placed on top of a white disk-shaped pellet. In Figure 25, the upper row shows a photograph of the lid of the firing container, and the lower row shows a photograph of the firing container itself and raw materials. The spider web-like film was observed in the Sr-laden configuration (second from the left) and in the two-layer structure, indicating that fibrous crystals grow in these configurations.

[0050] <Consideration of materials to replace part or all of Al> Sr ２ AlO ４ A portion of the Al in the above can be replaced with at least one of the following elements: Si, Ga, Ge, Zr, Ti. In other words, the aluminum sites can be partially substituted with Si, Ga, Ge, Zr, or Ti ions. Ga and Si have properties similar to Al, and theoretically, if Al can be partially substituted with Si, Ga, Ge, Zr, or Ti, the crystal structure can be softened, and it is thought that the electrical, magnetic, and optical properties can be improved.

[0051] <Sr ２ AlO ４ Application of Sr as a catalytic material in the oxidation reaction of benzyl alcohol ２ AlO ４The reaction temperature was 80°C, and the conversion rate was about 80%. The selectivity for esters was about 98%. Au / MgO was used as the catalyst material in the oxidation reaction of benzyl alcohol. In this case, the reaction temperature was 100°C, and the conversion rate was 100%. The selectivity for aldehydes was 2%, and the selectivity for esters was 98%. The catalyst turnover number (TON) was 7. Au / Ni-fiber was used as the catalyst material in the oxidation reaction of benzyl alcohol. The reaction temperature was 250°C, and the conversion rate was 93%. The selectivity for aldehydes was 99%. Au / CuO was used as the catalyst material in the oxidation reaction of benzyl alcohol. The reaction temperature was 80°C, and the conversion rate was 58.5%. The selectivity for aldehydes was 98.2%. The catalyst turnover frequency (TOF) was 56. Therefore, Sr was used as the catalyst material in the oxidation reaction of benzyl alcohol. ２ AlO ４ By using this catalyst, an ester selectivity of 98% was obtained at a low temperature of 80°C, which was not achieved with the other three catalysts.

[0052] Comparative Example 1: Sr ２ AlO ４ 26 is a flowchart showing a method for producing a crystalline compound according to a comparative example. First, in step S10, SrCO ３ , Al(OH) ３ , Eu ２ O ３ The materials are mixed. The mixing method is either hand mixing using a mortar or ball mill (BM, mechanical mixing). Figure 27 shows examples of hand mixing and ball mill. The left side of Figure 27 illustrates hand mixing using a mortar, and the right side illustrates the ball mill. In this example, the mixing time when hand mixing is used is 20 minutes, and when using a ball mill, the mixing time is 2 hours at 90 rounds / min.

[0053] Next, the process proceeds to step S12 in FIG. 26. In step S12, pre-firing is performed. Next, in step S14, the sample is subjected to isostatic pressing (CIP). The CIP conditions were 100 MPa and 5 minutes. A sample that underwent step S14 and a sample that omitted step S14 were prepared. Next, in step S16, main firing is performed. In one example, the firing conditions for the pre-firing in step S12 and the main firing in step S16 are 1000°C maintained in the atmosphere for 5 hours in the pre-firing, and 1300°C maintained in H ２ The following four samples were prepared for processing according to this flowchart: Sample 1: Hand-mixed, no CIP Sample 2: Hand-mixed, CIP Sample 3: BM, no CIP Sample 4: BM, CIP Figure 28 shows the results of X-ray diffraction measurements of Samples 1-4. All samples contained Sr １０ Al ６ O １９ and Sr ３ Al ２ O １２ H １２ The generation of Sr was confirmed. ２ AlO ４ It was found that Sr:Eu could not be obtained. In the solid-phase method typically used for synthesizing phosphors, all raw materials are mixed in advance and then fired by CIP. ２ AlO ４ Figure 29 shows photographs of Sample 2 (hand-mixed, with CIP) and Sample 4 (BM, with CIP) when irradiated with ultraviolet light. A slight green light emission was observed in both samples.

[0054] Comparative Example 2 In Comparative Example 2, a sample was produced using basically the same production process as in Comparative Example 1, but the Al(OH) ３ Al ２ O ３ FIG. 30 shows the results of X-ray diffraction measurements of four samples according to Comparative Example 2. The results were similar to those of Comparative Example 1. In the manufacturing process of Comparative Example 2, Sr ２ AlO ４ : It was found that Eu could not be obtained.

[0055] In addition, Ba, Ca, Mg, Eu, and materials that can be used in place of Eu, which are materials that can substitute for Sr in the above-mentioned oxide crystalline compounds, exist as ions, but for the sake of convenience, they are described simply as elements in some places. The degree to which materials that can be used in place of Ba, Ca, Mg, Eu, and Eu can substitute for Sr depends on the valence and ionic radius. The substitution amount of rare earth Eu and transition metals, etc., varies depending on the properties of each ion. Eu exists as 2+ and 3+ ions, and when fired in a reducing atmosphere, Eu 2+ Eu ２＋ is Sr 2＋ Since Gd is the same as Sr, and the ionic radius is also close, it can be substituted in large amounts, for example, it is possible to substitute 20% of Sr. ２＋ It is difficult to substitute many ions into the Sr site. ２＋ There are ions that can replace the Ba, and those that cannot are present in the interstitial spaces or precipitate as impurities. ２＋ , Ca ２＋ , Mg ２＋ The ion is Sr ２＋ Since it is close to the original, it is easy to replace, and replacement of 0-100% is possible.

[0056] The crystalline compounds described above are expected to be useful in a variety of applications, including as catalyst materials with reduced dependency on rare metals, efficient hydrogen generation without or with reduced use of rare metals, catalyst materials capable of chemical reactions with low environmental impact, and materials for magnetic or light-emitting devices.

Claims

1. A crystalline compound represented by the following composition formula (1), in which x is 1.6 or more and 2.1 or less, and y is 3.1 or more and 4.1 or less. Sr Ｘ AlO ｙ (1) 2. The crystalline compound of claim 1, wherein said crystalline compound is a ferromagnetic material having a Curie point of about 900K.

3. The crystalline compound of claim 1, wherein the chemical state of oxygen in said crystalline compound comprises a valence of -1.

4. The crystalline compound according to claim 1, which behaves as a ferromagnetic material due to the action of p orbitals of O ions.

5. The crystalline compound of claim 1, wherein the crystalline compound contains ions of Eu, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Cr, Mn, Fe, Co, Ni, or Cu.

6. The crystalline compound of claim 1, wherein the crystalline compound contains ions of Ba, Ca, or Mg.

7. The crystalline compound according to claim 1, wherein the crystalline compound is a single crystal semiconductor.

8. The Sr Ｘ AlO ｙ One O site in the formula is bonded to one Al and three Sr. Ｘ AlO ｙ The crystalline compound according to claim 1 , wherein the O sites other than the one O site included in the compound are bonded to one Al and four Sr.

9. The Sr Ｘ AlO ｙ 2. The crystalline compound according to claim 1, wherein one O site contained in the crystalline compound contains several percent of oxygen vacancies.

10. The crystalline compound of claim 1, wherein the crystalline compound is an elastic mechanoluminescent material, a luminescent material, or a catalytic material.

11. A crystalline compound having a first O site bonded to one Al and bonded to a first Sr group which is four Sr, a second O site bonded to one Al and bonded to a second Sr group which is four Sr, a third O site bonded to one Al and bonded to a third Sr group which is four Sr, and a fourth O site bonded to one Al, bonded to a fourth Sr group which is three Sr, and bonded to a remote Sr which is one Sr, wherein a bond length between the first Sr group and the first O site, a bond length between the second Sr group and the second O site, a bond length between the third Sr group and the third O site, and a bond length between the fourth Sr group and the fourth O site are within a predetermined specific range, and a bond length between the remote Sr and the fourth O site is longer than an upper limit value of the specific range.

12. A method for producing a crystalline compound, comprising heating a pellet formed by pressing powder containing an Al compound and an Eu compound together with a Sr compound to 1300-1900°C in a reducing atmosphere and then slowly cooling the mixture.

13. The method of claim 12, wherein the Sr compound is in the form of pressed pellets or powder spread in a sintering vessel.

14. The method of claim 12, wherein the crystalline compound is formed on the surface of the pellet, and the preferred growth orientation of the crystalline compound is [110].

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