Yoshiyuki Inaguma

Perovskites with Bi or Pb on the A site host a number of interesting and yet to be understood phenomena such as negative thermal expansion in BiNiO3. We employ hard x-ray photoemission spectroscopy of Ni 2p core level as well as valence band to probe the electronic structure of BiNiO3 and PbNiO3. The experimental results supported by theoretical calculations using dynamical mean-field theory reveal essentially identical electronic structure of the Ni-O subsystem typical of Ni2+ charge-transfer insulators. The two materials are distinguished by filling of the Bi(Pb)-O antibonding states in the vicinity of the Fermi level, which is responsible for the Bi disproportionation in BiNiO3 at ambient pressure and absence of similar behavior in PbNiO3. The present experiments provide evidence for this conclusion by revealing the presence/absence of Bi/Pb 6s states at the top of the valence band in the two materials.

We prepared high-purity Sr1-xBaxFeO2F by a low-temperature fluorination method, investigated the average structure by synchrotron X-ray diffraction (SXRD), and measured second harmonic generation (SHG) in this material. For BaFeO2F, the average and local structures were investigated by time-of-flight (TOF) neutron diffraction and the X-ray pair distribution function (PDF), respectively. In addition, the magnetic moment under a magnetic field was measured. SHG was observed for Sr1-xBaxFeO2F (x = 1.0, 0.9, and 0.7) and was below the detection limit for x = 0.5. The average crystal structure of BaFeO2F was determined by the refinement of the TOF neutron diffraction data to be a cubic structure in which Fe3+ ions are displaced to (x, x, 1/2) off-site positions with a 1/12 occupancy. The magnetic structure was a G-type antiferromagnetic structure, and the magnetic moments of the Fe3+ ion were 3.84 and 3.50 μB at 3 and 300 K, respectively. According to the X-ray PDF analysis, the local structure was not a cubic structure with the equivalent displacement of the Fe3+ ion to the off-site positions but a noncentrosymmetric structure in which Fe3+ ions are displaced in various directions in distorted BX6 octahedra. These local polar domains induce the SHG. The coexistence of polar domains with different polarization directions results in a cubic average structure. The formation of local polar domains was supported by the canted ferromagnetic components observed in magnetic moment measurements carried out under an applied magnetic field.

We synthesized a perovskite-type RbNbO3 at 1173 K and 4 GPa from non-perovskite RbNbO3 and investigated its crystal structure and properties towards ferroelectric material design. Single-crystal X-ray diffraction analysis revealed an orthorhombic cell in the perovskite-type structure (space group Amm2, no. 38) with a = 3.9937(2) Å, b = 5.8217(3) Å, and c = 5.8647(2) Å. This non-centrosymmetric space group is the same as the ferroelectric BaTiO3 and KNbO3 but with enhanced distortion. Structural transition from orthorhombic to two successive tetragonal phases (Tetra1 at 493 K, Tetra2 at 573 K) was observed, maintaining the perovskite framework before reverting to the triclinic ambient phase at 693 K, with no structural changes between 4 and 300 K. The first transition is similar to that of KNbO3, whereas the second to Tetra2, marked by c-axis elongation and a significant cp/ap ratio jump (from 1.07 to 1.43), is unique. This distortion suggests a transition similar to that of PbVO3, where an octahedron's oxygen separates along the c-axis, forming a pyramid. Ab initio calculations simulating negative pressure like thermal expansion predicted this phase transition (cp/ap = 1.47 at -1.2 GPa), aligning with experimental findings. Thermal analysis revealed two endothermic peaks, with the second transition entailing a greater enthalpy change and volume alteration. Strong second harmonic generation signals were observed across Ortho, Tetra1, and Tetra2 phases, similar to BaTiO3 and KNbO3. Permittivity increased during the first transition, although the second transition's effects were limited by thermal expansion-induced bulk sample collapse. Perovskite-type RbNbO3 emerges as a promising ferroelectric material.

Li4B7O12Cl, Li4B4Al3O12Cl, and new boracite, Li4B4Al3O12Cl1-xBrx (x = 0.1, 0.2 and 1.0) were synthesized using solid-state reaction method. The crystal structures of Li4B7O12Cl and Li4B4Al3O12Cl were investigated through high-intensity synchrotron X-ray diffraction (SXRD) analysis. The ionic conductivity was elucidated for the ceramics and green compacts to discuss their potential as a solid electrolyte of all-solid-state Li-ion batteries. The ionic conductivity of the bulk part was 2.0 × 10−5 S/cm for Li4B4Al3O12Cl0.2Br0.1 and Li4B4Al3O12Cl0.8Br0.2 at 294 K and the total ionic conductivity of these compounds was approximately 10−8 S/cm. Furthermore, we succeeded to prepare a high-density green compact for Li4B7O12Cl. The total ionic conductivity of this sample was higher than that of Li4B7O12Cl glass-ceramics at high temperatures. The conduction pathway was determined by bond valence sum mapping for Li4B7O12Cl and Li4B4Al3O12Cl, which was conducted based on the refined structural data of the high-intensity SXRD data. The results showed that an additional conduction pathway is formed for Li4B4Al3O12Cl and its larger unit cell promotes Li+ migration around the halogen ion. Although the substitution of Cl− with Br− suppresses the migration of Li+ around halogen ion due to the large ionic radius of Br− in Li4B4Al3O12Cl1-xBrx, appropriate substitution enhances ion migration via the additional pathway without suppressing the ion transfer around the halogen ion. Thus, Li4B4Al3O12Cl0.2Br0.1 and Li4B4Al3O12Cl0.8Br0.2 showed high ionic conductivity.

Immobilization of phosphotungstate ([PW12O40](3-)) in the interlayer space of a Mg-Al layered double hydroxide (LDH) resulted in an absorption edge at similar to 350 nm, different from the pristine LDH or the POM (either in aqueous solution or in the solid state). The obtained hybrid showed enhanced photocatalytic activity for water oxidation in the presence of Ag+ as an electron acceptor.

We attempted to synthesize complex metal fluorides via reaction between metal and solid-state fluorine sources and succeeded in preparing trirutile-type Li2MoF6 using LiF, the metal Mo, and CuF2. We also found a new phase of Li2MoF6 that is isostructural with trigonal Li2ZrF6 via a combination of solid-state fluorine sources and high-pressure synthesis. The reaction occurs exothermically and involves conversion and addition associated with redox reaction, and CuF2 then functions as both an oxidizing agent and fluorine source. Because the overall reaction proceeds stoichiometrically, the required amount of fluorine can be controlled by the amount of solid-state fluorine agents. The synthesis route was also applicable for the preparation of other known fluorides, Li2MF6 (M = Ti, Zr, and Nb) and β-Li3MF6 (M = Ti and V). The synthetic route using a solid-state fluorine source is suitable for the exploration of novel inorganic complex metal fluorides.

<p>The PbFeO₂F serves as a bifunctional material for a water-oxidation photoanode workable under a wide range of visible light and a water-oxidation electrocatalyst operatable at a relatively low overpotential.</p>

<p>New Sillén–Aurivillius layered oxychlorides with triple-, quadruple- and quintuple-perovskite layers (<italic>n</italic> = 3−5) are successfully synthesized and their photocatalytic activities are enhanced with increasing the number of the perovskite layers.</p>

<p>A mechanochemical synthesis was developed to generate a highly active electrocatalyst featuring catalytic cobalt sites embedded within an electron-withdrawing fluorophosphate host.</p>

<p>The first example of both cation- and anion-ordered rutile-type derivative LiTeO₃(OH) (= HLiTeO₄) has been discovered. LiTeO₃(OH) belongs to a non-centrosymmetric space group <italic>P</italic>2₁.</p>

<p>A synthetic approach involving the HSAB principle provided the perovskite-type oxyfluoride AgTiO₂F.</p>

Most perovskite-type oxyfluorides have a cubic structure even though the tolerance factors of these compounds are not unity. In this study, new perovskite-type oxyfluorides, BaInO2F, with a tolerance factor less than unity was synthesized and its crystal structure was compared with other perovskite-type oxyfluorides. In addition, its local structure was investigated using the atomic pair distribution function (PDF) technique. BaInO2F was synthesized by a low-temperature fluorination method, and its structure was cubic with an abnormally large displacement factor of anions. By comparing the structures of various perovskite-type oxyfluorides, we found that the ion species showing abnormally large displacement factor varied with the tolerance factors. In the case of BaFeO2F, the abnormally large displacement factor of the B-site ion, Fe3+, originated from the displacement of the Fe3+ ion from the center of a BX6 octahedron along < 110 > direction. According to the PDF analysis, the local structure of BaInO2F was not cubic but a triclinic system with tilted and distorted BX6 octahedra. On the basis of these results, we considred that the structure of oxyfluorides with a tolerance factor less than unity was relaxed by the tilt of the octahedra, similar to perovskite-type oxides. The long-range order of the anion displacements, however, was suppressed by the structural disorder arising from the random distribution of oxide and fluoride ions, therefore the average structure observed by diffraction methods was predicted to be a cubic structure.

Polycrystalline NASICON-type Li-ion conductor LiZr2(PO4)3 (LZPO) with different ratios of Li isotopes, namely 6LiZr2(PO4)3 (6-LZPO), 7LiZr2(PO4)3 (7-LZPO), and LZPO with the natural Li isotope ratio (n-LZPO), has been synthesized by a conventional solid state reaction. The phase transformation as a function of temperature between the low-temperature triclinic phase, which exhibits lower Li-ion conductivity, and high-temperature rhombohedral phase, which exhibits higher Li-ion conductivity, has been evaluated by powder X-ray diffraction (XRD), electron diffraction, and differential scanning calorimetry (DSC) measurements. According to XRD and DSC measurements, the phase transition temperature decreases in the order 6-LZPO &gt n-LZPO ≈ 7-LZPO. The dependence of phase transition temperature on the Li isotope implies that Li ions have a strong effect on phase stability. The phase transition is primarily related to the change in configuration entropy of Li ions in LZPO.

We have investigated high-pressure, high-temperature phase transitions of spinel (Sp)-type MgV2O4, FeV2O4, and MnCr2O4. At 1200-1800 °C, MgV2O4 Sp decomposes at 4-7 GPa into a phase assemblage of MgO periclase + corundum (Cor)-type V2O3, and they react at 10-15 GPa to form a phase with a calcium titanite (CT)-type structure. FeV2O4 Sp transforms to CT-type FeV2O4 at 12 GPa via decomposition phases of FeO wüstite + Cor-type V2O3. MnCr2O4 Sp directly transforms to the calcium ferrite (CF)-structured phase at 10 GPa and 1000-1400 °C. Rietveld refinements of CT-type MgV2O4 and FeV2O4 and CF-type MnCr2O4 confirm that both the CT- and CF-type structures have frameworks formed by double chains of edge-shared B3+O6 octahedra (B3+ = V3+ and Cr3+) running parallel to one of orthorhombic cell axes. A relatively large A2+ cation (A2+ = Mg2+, Fe2+, and Mn2+) occupies a tunnel-shaped space formed by corner-sharing of four double chains. Effective coordination numbers calculated from eight neighboring oxygen-A2+ cation distances of CT-type MgV2O4 and FeV2O4 and CF-type MnCr2O4 are 5.50, 5.16, and 7.52, respectively. This implies that the CT- and CF-type structures practically have trigonal prism (six-coordinated) and bicapped trigonal prism (eight-coordinated) sites for the A2+ cations, respectively. A relationship between cation sizes of VIIIA2+ and VIB3+ and crystal structures (CF- and CT-types) of A2+B2 3+O4 is discussed using the above new data and available previous data of the postspinel phases. We found that CF-type A2+B2 3+O4 crystallize in wide ionic radius ranges of 0.9-1.4 Å for VIIIA2+ and 0.55-1.1 Å for VIB3+, whereas CT-type phases crystallize in very narrow ionic radius ranges of ∼0.9 Å for VIIIA2+ and 0.6-0.65 Å for VIB3+. This would be attributed to the fact that the tunnel space of CT-type structure is geometrically less flexible due to the smaller coordination number for A2+ cation than that of CF-type.

Heat capacity (CP) of rutile and α-PbO2 type TiO2 (TiO2-II) were measured by the differential scanning calorimetry and thermal relaxation method. Using the results, standard entropies at 1 atm and 298.15 K of rutile and TiO2-II were determined to be 50.04(4) and 46.54(2) J/mol K, respectively. Furthermore, thermal expansivity (α) determined by high-temperature X-ray diffraction measurement and mode Grüneisen parameters obtained by high-pressure Raman spectroscopy suggested the thermal Grüneisen parameter (γth) for TiO2-II of 1.7(1). By applying the obtained low-temperature CP and γth, the measured CP and α data of TiO2-II were extrapolated to higher temperature region using a lattice vibrational model calculation, as well as rutile. Internally consistent thermodynamic data sets of both rutile and TiO2-II assessed in this study were used to thermodynamically calculate the rutile‒TiO2-II phase equilibrium boundary. The most plausible boundary was obtained to be P (GPa) = 0.0074T (K) − 1.7. Our boundary suggests that the crystal growth of TiO2-II observed below 5.5 GPa and 900 K in previous studies advanced in its stability field. The phase boundary calculation also suggested small, exothermic phase transition enthalpy from rutile to TiO2-II at 1 atm and 298.15 K of − 0.5 to − 1.1 kJ/mol. This implies that the thermodynamic stability of rutile at 1 atm above room temperature is due to larger contribution of entropy term.

(1-x)KNbO3-xKMgF3 was synthesized using a sealed silica tube with an oxygen generator (KNMOF-O2) or a high-pressure and high-temperature apparatus (KNMOF-hp). The variations in phase transition temperature and dielectric properties were investigated. The temperatures of a tetragonal-to-cubic phase transition and an orthorhombic-to-tetragonal phase transition decreased with x, whereas the temperature of a rhombohedral-to-orthorhombic phase transition increased with it. The temperature variation, however, became constant for x ≥ 0.05 and did not merge into one. In the temperature dependence of dielectric permittivity for x = 0.05 (KNMOF-hp), a broad maximum was observed in the vicinity of 400 K and its value reached approximately 2200 which is higher than that of a KNbO3 dense ceramic. Considering the variation of phase transition temperatures and dielectric measurements, it is concluded that the relaxor-like behavior was realized for x = 0.05 (KNMOF-hp).

Unlike X-ray diffraction or Raman techniques, which suffer from low spatial resolution, transmission electron microscopy can be used to obtain strain maps of nanoscaled materials and devices. Convergent-beam electron diffraction (CBED) and nanobeam electron diffraction (NBED) techniques detect the deviation of a lattice constant (i.e. an indicator of strain) within 0.01% however, their use is restricted to beam-insensitive samples. Selected-area electron diffraction (SAED) does not have such limitations but has low spatial resolution and precision. The use of a spherical aberration corrector and a nanosized selected-area aperture improves the spatial resolution, but the precision is still low. In this study, a two-dimensional stage-scanning system is used to acquire arrays of diffraction patterns at different positions of the sample under fixed beam conditions. Data processing with iterative nonlinear least-squares fitting enabled the spot displacement for each point of the scan area to be measured with precision comparable to that of the CBED or NBED technique. The precise strain determination, in combination with the simplicity of the measurement process, makes the nanosized SAED technique competitive with other methods for strain mapping at nanoscale dimensions.

Perovskite oxides hosting ferroelectricity are particularly important materials for modern technologies. The ferroelectric transition in the well-known oxides BaTiO3 and PbTiO3 is realized by softening of a vibration mode in the cubic perovskite structure. For most perovskite oxides, octahedral-site tilting systems are developed to accommodate the bonding mismatch due to a geometric tolerance factor t = (A-O)/[√2(B-O)] &lt 1. In the absence of cations having lone-pair electrons, e.g., Bi3+ and Pb2+, all simple and complex A-site and B-site ordered perovskite oxides with a t &lt 1 show a variety of tilting systems, and none of them become ferroelectric. The ferroelectric CaMnTi2O6 oxide is, up to now, the only one that breaks this rule. It exhibits a columnar A-site ordering with a pronounced octahedral-site tilting and yet becomes ferroelectric at Tc ≈ 650 K. Most importantly, the ferroelectricity at T &lt Tc is caused by an order-disorder transition instead of a displacive transition this character may be useful to overcome the critical thickness problem experienced in all proper ferroelectrics. Application of this new ferroelectric material can greatly simplify the structure of microelectronic devices. However, CaMnTi2O6 is a high-pressure phase obtained at 7 GPa and 1200 °C, which limits its application. Here we report a new method to synthesize a gram-level sample of ferroelectric Ca2-xMnxTi2O6, having the same crystal structure as CaMnTi2O6 and a similarly high Curie temperature. The new finding paves the way for the mass production of this important ferroelectric oxide. We have used neutron powder diffraction to identify the origin of the peculiar ferroelectric transition in this double perovskite and to reveal the interplay between magnetic ordering and the ferroelectric displacement at low temperatures.

Gallium oxynitride (GaON) nanoparticles were synthesized through three steps (i) hydrothermal treatment of an aqueous solution containing Ga(NO3)3, hexamethylenetetramine (HMT), and acetylene black, (ii) calcination, and (iii) nitridation. The presence of acetylene black in the hydrothermal treatment is effective for the synthesis of Ga2O3 nanoparticles after the calcination. The intermediate obtained after the hydrothermal reaction possessed no detectable Ga particles in the TEM observation, although the presence of Ga was confirmed in the EDS measurement. This means that acetylene black (AB), in this study, cannot play a simple role as a template. The GaON nanoparticles obtained from the Ga2O3 nanoparticles through nitridation possessed a higher oxygen content than that from Ga2O3 obtained by hydrothermal synthesis without acetylene black and the subsequent calcination. The obtained GaON nanoparticles show higher photocatalytic NOx decomposition activity than bulk GaON synthesized under the same conditions except without acetylene black in the hydrothermal reaction, because of the longer absorption edge and the higher specific surface area. In addition, the effect of nitridation temperature and time on the obtained GaON nanoparticles and their photocatalytic activity was also investigated. Consequently, nanoparticle morphology of a precursor for GaON is important not only for high surface area but also for high visible-light response.

We investigated a new one-pot synthesis method for ss-TaON oxynitride using (C6N9H3)(n) (melon) as a solid nitrogen source. ss-TaON single phase was obtained from Ta2O5 using melon heating under a separated and sealed condition in a quartz glass tube. The oxygen and nitrogen contents of prepared ss-TaON were almost 100% of the theoretical values.

The LiNbO3 (LN)-type oxynitrides, MnTaO2N and (1 - x) MnTaO2N-xMn(4)Ta(2)O(9) were synthesized under high pressures and at high temperatures. The new LN-type oxynitride, Mn(Mn1/6Ta5/6)O2.5N0.5 (0.75MnTaO(2)N-0.25Mn(4)Ta(2)O(9)) could be obtained with trace impurities. In this compound, the displacement of B ion (Ta/Mn ion) from the center of the BX6 octahedron was smaller than that in other LN-type oxides containing Ta and/or Mn ions. This indicates that the displacement of Ta/Mn ion was reduced by doping with nitride ion.

The compound Mn2[VO4]F was synthesized using a hydrothermal synthesis route at low temperature and its crystal structure was determined from single crystal X-ray diffraction data. Mn2[VO4]F was characterized by magnetic susceptibility and specific heat capacity measurements. Mn2[VO4]F crystallizes with the triplite-type structure, space group C2/c, a = 13.451(3) Å b = 6.6953(16) Å c = 10.126(3) Å β = 116.587(4)° V = 815.6(3) Å3 and Z = 8. The structure consists of a 3D-framework built up of VO4 tetrahedra, and manganese (II) polyhedra which form chains running along the [101] and [010] directions. The coordination of the manganese cations and the connectivity between the manganese polyhedra are not defined clearly due to the disorder of the fluoride anions which form zigzag chains along [001]. The magnetic susceptibility follows a Curie–Weiss behavior above 50 K with Θ = −88 K indicating that predominant magnetic interactions are antiferromagnetic. The specific heat capacity and magnetization measurements show that Mn2[VO4]F undergoes a three-dimensional magnetic ordering at TN = 30 K and a canted weak ferromagnetism due to mixed-anion effect.

High-pressure high-temperature phase relation experiments in Mg14Si5O24 were performed using a 6-8 multi-anvil high-pressure apparatus in the pressure range of 12-22 GPa and temperature range of 1673-2173 K. We first found that Mg14Si5O24 anhydrous phase B (Anh-B) dissociates to Mg2SiO4 wadsleysite (Wd) and MgO periclase (Per) at about 18 GPa and 1873 K. From the results of the high-pressure experiments, the phase boundaries of 5 Mg2SiO4 forsterite (Fo) + 4 Per = Anh-B and Anh-B = 5 Wd + 4 Per were determined. In addition, the isobaric heat capacity (CP) of Anh-B was measured by differential scanning calorimetry in the temperature range of 300-770 K and the thermal relaxation method using a Physical Property Measurement System (PPMS) in the range of 2-303 K. From the measured low-temperature C-P, the standard entropy (S-298.15 degrees) of Anh-B was determined to be 544.4(2) J/(mol . K). We also performed high-temperature X-ray diffraction measurements in the range 303-773 K to determine the thermal expansivity (a) of Anh-B. The obtained CP and a were theoretically extrapolated to higher temperature region using a lattice vibrational model calculation partly based on Raman spectroscopic data. Thermodynamic calculations by adopting the thermochemical and thermoelastic data for Anh-B obtained in this study and the estimated formation enthalpy for Anh-B of -13 208 kJ/mol gave phase equilibrium boundaries for 5 Fo + 4 Per = Anh-B and Anh-B = 5 Wd + 4 Per that were consistent with those determined by the present high-pressure high-temperature experiments. The results clarified that, in the Mg14Si5O24 system, Anh-B is stable between 12 and 18 GPa at the expected temperatures of the Earth's mantle.

Strong near-infrared luminescence under ultraviolet excitation was obtained in epitaxially grown BaSnO3 perovskite films. The films were grown on SrTiO3 (001) substrates by pulsed-laser deposition, and the crystallinity of the epitaxial growth was confirmed by X-ray diffraction and reflected high-energy electron diffraction. Near-infrared luminescence of the as-grown film showed a broad emission peak centered at 905 nm. The transparencies of the double-side-polished substrate with and without the film were about 70% at around 550 nm, suggesting that the transparency of the film itself is close to 100%. The preparation of epitaxial thin films with a strong near-infrared luminescence and a high transparency may open up applications for wavelength conversion in solar cells for realizing a higher efficiency. Published by AIP Publishing.

To understand luminescent mechanisms of lanthanide (Ln) doped phosphors, it is important to know the energy positions of unoccupied Ln(2+) 4f and Ln(3+) 5d states, as well as occupied Ln(3+) 4f states, relative to the energy bands of host materials. Photoluminescence excitation (PLE) spectra of Ln doped YAlO3 were measured in a vacuum ultraviolet (VUV) region and the energy positions of Ln(2+) 4f and Ln(3+) 5d states in the wide-gap YAlO3 were elucidated. Peaks assignable to host lattice excitation were observed in all samples at approximately 8 eV in the PLE spectra. PLE peaks derived from charge transfer (CT) and 4f-5d transitions were observed at lower energy than the bandgap energy. Ln(2+) 4f energy levels were obtained from the PLE peak energies for the CT transitions along with the valence band maximum. In contrast, Ln(3+) 5d energy levels were evaluated from those for the 4f-5d transitions along with the Ln(3+) 4f energy levels, which were obtained previously from X-ray photoelectron spectroscopy measurements. The elucidated Ln(2+) 4f and Ln(3+) 5d energy levels were exhibited in an energy diagram together with Ln(3+) 4f energy levels and host energy bands. The experimental Ln(2+) 4f and Ln(3+) 5d energy levels were in good agreement with the reported theoretical data. (C) 2017 Elsevier B.V. All rights reserved.

Perovskite PbCoO3 synthesized at 12 GPa was found to have an unusual charge distribution of Pb(2+)Pb(3)(4+)Co(2+)2Co(2)(3+)O(12) with charge orderings in both the A and B sites of perovskite ABO(3). Comprehensive studies using density functional theory (DFT) calculation, electron diffraction (ED), synchrotron X-ray diffraction (SXRD), neutron powder diffraction (NPD), hard X-ray photoemission spectroscopy (HAXPES), soft X-ray absorption spectroscopy (XAS), and measurements of specific heat as well as magnetic and electrical properties provide evidence of lead ion and cobalt ion charge ordering leading to Pb2+Pb34+Co22+Co23+O12 quadruple perovskite structure. It is shown that the average valence distribution of Pb3.5+Co2.5+O3 between Pb3+Cr3+O3 and Pb4+Ni2+O3 can be stabilized by tuning the energy levels of Pb 6s and transition metal 3d orbitals.

Phase relations in FeTiO3 were precisely determined at 25-35 GPa and 600-1600 A degrees C using multianvil high-pressure experiments with tungsten carbide anvils. Pressure generation up to about 36 GPa at 1600 A degrees C was evaluated using Al2O3 solubility in MgSiO3 perovskite (Pv) in the system MgSiO3-Al2O3. At about 28 GPa, FeTiO3 Pv dissociates into an assemblage of calcium titanate (CT)-type Fe2TiO4 + orthorhombic-I (OI)-type TiO2 below 1200 A degrees C. However, above 1200 A degrees C at 28 GPa, FeTiO3 Pv decomposes into a new, denser phase assemblage of CT-type Fe2TiO4 + a new compound of FeTi2O5. The new phase FeTi2O5 was recovered as an amorphous phase at 1 atm. In situ X-ray diffraction experiments at 35.1 GPa indicated that the new phase (N-p) FeTi2O5 has orthorhombic symmetry with cell parameters a = 8.567(2) a"&lt;&lt;, b = 5.753(1) a"&lt;&lt; and c = 5.257(1) a"&lt;&lt;. In addition, the assemblage of CT-type Fe2TiO4 + OI-type TiO2 changes to FeO wustite (Wu) + OI-type TiO2 at about 33 GPa below 1000 A degrees C. The phase assemblages in FeTiO3 are denser in the order: FeTiO3 (Pv) -&gt; 1/2Fe(2)TiO(4) (CT) + 1/2TiO(2) (OI) -&gt; 1/3Fe(2)TiO(4) (CT) + 1/3FeTi(2)O(5) (N-p) -&gt; FeO (Wu) + TiO2 (OI). Our results indicate that the upper stability limit of FeTiO3 Pv is about 28 GPa at 600-1600 A degrees C. This puts a constraint on peak shock pressure for formation of naturally discovered lithium niobate-type FeTiO3 which was interpreted to be retrograde transition product of FeTiO3 Pv on release of shock pressure.

The solid state oxide Li-ion conductors with high electrochemical stability as well as high ionic conductivity are needed for application to all-solid-state Li-ion battery. In this study, A(3)Li(x)Ta(6 - x)Zr(x)Si(4)O(26) (A = Sr and Ba) as the candidate solid electrolytes stable against Li metal were synthesized by a conventional solid state reaction, and their structure and ionic conductivities were investigated. Both the compounds with A = Sr and Ba crystallize in hexagonal structure with space group P (6) over bar 2m in the same as A(3)Ta(6)Si(4)O(26) does. MEM analysis, first principles calculation, and NMR spectroscopy showed that Li ions reside in interstitial sites. The sample with A = Ba exhibits higher ionic conductivity (e.g. 6.9 x 10(-8) S cm(-1) at 500 K in x = 1.0) than that with A = Sr (e.g. 3.2 x 10(-8) S cm(-1) at 500 K in x = 1.0). Ionic conductivity was enhanced with an increase of the substitution of Li and Zr. Further enhancement of ionic conductivity was derived by making deficiencies at A site cation. Consequently, Ba2.75Li1.5Ta5ZrSi4O26 exhibits the highest total ionic conductivity of 4 x 10(-7) S/cm at 500 K and the lowest activation energy of 0.72 eV. The consideration of the size of bottlenecks and nudged elastic band calculations suggest that Li ions diffuse in the A-site deficient layer perpendicular to the c-axis. (C) 2015 Elsevier B.V. All rights reserved.

Structure and valence state change of Li2RuO3 and ruthenium-substituted lithium manganese oxide, Li2Mn0.4Ru0.6O3 (LMR), with layered structure were investigated using Synchrotron X-ray diffraction (SXRD) and X-ray absorption spectroscopy measurements before and after electrochemical cycling. The charge-discharge voltage curves of both LMR and Li2RuO3 significantly vary in the subsequent cycle. The SXRD Rietveld structural refinements demonstrate that the LMR undergoes irreversible structural transition. The Mn K-edge spectra confirm the structural modification in the MnO6 octahedra with Li de-intercalation. The Ru L-edge spectra for LMR show similar behavior to Li2RuO3 during electrochemical cycling. These spectra appear reductive peak shift on the way to charging to 4.8 V. The phenomena are not attributed to the reduction of hexavalent Ru to pentavalent but a variation of the splitting between bonding and anti-bonding e(g) orbitals. The charge-discharge reactions mechanism of LMR and Li2RuO3 are discussed. (C) 2015 Elsevier B.V. All rights reserved.

Perovskite-type oxides with a chemical formula of ABO3 exhibit various functional properties. Among them, lithium ion-conducting oxides with A-site deficient perovskite-type structure such as La2/3－xLi3xTiO3 show fast lithium ion conductivity of 10－5 to 10－3 S/cm at room temperature. The high conductivity is attributable to the percolation-controlled diffusion of lithium ions in the vicinity of A-site via vacancy. In this report, recent research on perovskite-type lithium ion-conducting oxides are reviewed in terms of crystal structure including microstructure, and chemical bond. The relationship among structure, chemical bond, especially second-order Jahn-Teller effect attributable to the covalent bond between B ion with d0 electronic configuration and O ion, and lithium-ion diffusion are discussed.

A novel LiNbO3-type (LN-type) lead zinc oxide, PbZnO3, was successfully synthesized under high pressure and temperature. Rietveld structure refinement using synchrotron powder X-ray diffraction (XRD) data demonstrated that LN-type PbZnO3 crystallized into a trigonal structure with a polar space group (R3c). The bond valence sum estimated from the interatomic distances indicated that the sample possesses a Pb4+Zn2+O3 valence state. Polarization could evolve as a result of the repulsion between constituent cations because PbZnO3 does not contain a stereochemical 6s(2) cation or a Jahn-Teller active d(0) cation. Distortion of ZnO6 octahedra resulting from cation shift is comparable with that of d(0) TiO6 in ZnTiO3 and MnTiO3 with LN-type oxides, which leads to stabilization of the polar structure. PbZnO3 exhibited metallic behavior and temperature-independent diamagnetic character. In situ XRD measurement revealed that the formation of LN-type PbZnO3 occurred directly without the formation of a perovskite phase, which is unusual among LN-type materials obtained by high-pressure synthesis.

Capacity and voltage retentions upon subsequent cycles for Li2RuO3 and Li2Mn0.4Ru0.6O3 (LMR) under various cutoff voltages have been investigated. The change in average and local structures upon electrochemical cycling were examined by ex-situ XRD and Ru L-3-edge XANES measurements, and the relationship between the cyclic capabilities and the structural changes is discussed. The deteriorations of discharge capacity and average discharge voltage in the subsequent cycles of LMR with a charge cut-off voltage of 4.8 V vs. Li/Li+ are remarkably smaller than that with the voltage of 4.2 V. Moreover, LMR exhibits higher average discharge voltage than Li2RuO3 under a charge cut-off voltage of 4.8V. The phase transition behavior of LMR was not similar to Li2RuO3 upon electrochemical cycling. Ru L-3-edge XANES spectra measurements reveal that RuO6 octahedra in LMR charged at 4.2V are much distorted. The local structure of RuO6 octahedra is associated with the cyclic capability of LMR and Li2RuO3. (C) The Electrochemical Society of Japan, All rights reserved.