稲熊 宜之

Thin films of YAlO3: Gd3+ and YAlO3: Gd3+-Pr3+ were prepared on LaAlO3 (001) single crystal substrates by pulsed laser deposition (PLD). Both films were grown epitaxially and their surfaces were uniformly smooth. Under UV excitation at 216 nm, YAlO3: Gd3+ film did not show any intense photoluminescence (PL); on the other hand, YAlO3: Gd3+-Pr3+ film showed intense Gd3+ PL at 314 nm through Pr3+ 4f-5d absorption. Under electron irradiation with acceleration of 2.00 kV, both films showed UV cathodo luminescence (CL) from Gd3+ ions. In contrast to PL, the CL intensity of the YAlO3: Gd3+ film was four times greater than that of the YAlO3: Gd3+-Pr3+ film. The PL excitation spectrum of YAlO3: Gd3+ in vacuum UV region revealed the presence of an intense excitation band at 155 nm assignable to YAlO3 host absorption. This observation implied that the energy of accelerated electrons was absorbed by the host and then transferred to Gd3+. Pr3+ co-doping was found to weaken the Gd3+ emission in CL because the excitation energy absorbed by the host was transferred to not only Gd3+ but also Pr3+ accompanying visible emission and nonradiative transition in Pr3+. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

We determined phase relations in MgCr2O4 at 12-28 GPa and 1000-1600 degrees C using a multi-anvil apparatus. At 12-15 GPa, spinel-type MgCr2O4 (magnesiochromite) first decomposes into a mixture of new Mg2Cr2O5 phase + corundum-type Cr2O3 at 1100-1600 degrees C, but it dissociates first into MgO periclase + corundum-type Cr2O3 at 1000 degrees C. At about 17-19 GPa, the mixture of Mg2Cr2O5 phase + corundum-type Cr2O3 transforms to a single MgCr2O4 phase. Structure refinements using synchrotron X-ray powder diffraction data indicated that the high-pressure MgCr2O4 phase has a CaTi2O4-type structure (Cmcm), and that the basic structure of the Mg2Cr2O5 phase is the same as that of recently found modified ludwigite-type Mg2Al2O5 and Fe2Cr2O5 (Pbam). The phase relations in this study may suggest that natural chromitites in the Luobusa ophiolite regarded as the deep-mantle origin were derived from the mantle shallower than the depths corresponding to pressure of 12-15 GPa because of absence of the assemblage of (Mg,Fe)(2)Cr2O5 + Cr2O3 in the chromitites.

The polycrystalline MO2's (HP-PdF2-type MO2, M = Rh, Os, Pt) with high-pressure PdF2 compounds were successfully synthesized under high-pressure conditions for the first time, to the best of our knowledge. The crystal structures and electromagnetic properties were studied. Previously unreported electronic properties of the polycrystalline HP-PdF2-type RuO2 and IrO2 were also studied. The refined structures clearly indicated that all compounds crystallized into the HP-PdF2-type structure, M4+O22-, rather than the pyrite-type structure, Mn+(O-2)(n-) (n < 4). The MO2 compounds (M = Ru, Rh, Os, Ir) exhibited metallic conduction, while PtO2 was highly insulating, probably because of the fully occupied t2g band. Neither superconductivity nor a magnetic transition was detected down to a temperature of 2 K, unlike the case of 3d transition metal chalcogenide pyrites.

The new compound HP-Na2Co[PO4]F was synthesized by high pressure solid state reaction and its crystal structure was determined from single crystal X-ray diffraction data. The physical properties of HP-Na2Co[PO4]F were characterized by magnetic susceptibility, specific heat capacity, galvanometric cycling, and electrochemical impedance spectroscopy measurements. HP-Na2Co[PO4]F crystallizes with the space group P6(3)/m, a = 10.5484(15), c = 6.5261(9) angstrom, V = 628.87(15) angstrom(3) and Z = 6. The crystal structure consists of infinite chains of edge-sharing CoF2O4 octahedra. The latter are interconnected through the PO4 tetrahedra forming a 3D-Co[PO4]F-framework. The six coordinated sodium atoms are distributed over three crystallographic sites (2b, 6h, and 4f). The structure of HP-[Na1(1/3)Na2(3/3)Na3(2/3)]Co[PO4]F is similar to [Na1(1/3)Na2(3/3)Sr3(1/3)rectangle(1/3)]Ge[GeO4]O. There is only one difference; Na3 occupies the 4f (1/3, 2/3, 0.0291) atomic position, whereas the Sr occupies the 2c (1/3, 2/3, 1/4) atomic position. The magnetic susceptibility follows a Curie-Weiss behavior above 50 K with Theta = -21 K indicating predominant antiferromagnetic interactions. The specific heat capacity and magnetization measurements show that HP-Na2Co[PO4]F undergoes a three-dimensional magnetic ordering at T-N = 11.0(1) K. The ionic conductivity sigma, estimated at 350 degrees C, is 1.5 X 10(-7) S cm(-1). The electrochemical cycling indicates that only one sodium ion could be extracted during the first charge in Na half-cell; however, the re-intercalation was impossible due to a strong distortion of the structure after the first charge to 5.0 V.

We determined phase relations in FeCr2O4 at 12-28 GPa and 800-1600 degrees C using a multi-anvil apparatus. At 12-16 GPa, FeCr2O4 spinel (chromite) first dissociates into two phases: a new Fe2Cr2O5 phase + Cr2O3 with the corundum structure. At 17-18 GPa, the two phases combine into CaFe2O4-type and CaTi2O4-type FeCr2O4 below and above 1300 degrees C, respectively. Structure refinements using synchrotron X-ray powder diffraction data confirmed the CaTi2O4-structured FeCr2O4 (Cmcm), and indicated that the Fe2Cr2O5 phase is isostructural to a modified ludwigite-type Mg2Al2O5 (Pbam). In situ high-pressure high-temperature X-ray diffraction experiments showed that CaFe2O4-type FeCr2O4 is unquenchable and is converted into another FeCr2O4 phase on decompression. Structural analysis based on synchrotron X-ray powder diffraction data with transmission electron microscopic observation clarified that the recovered FeCr2O4 phase has a new structure related to CaFe2O4-type. The high-pressure phase relations in FeCr2O4 reveal that natural FeCr2O4-rich phases of CaFe2O4- and CaTi2O4-type structures found in the shocked Suizhou meteorite were formed above about 18 GPa at temperature below and above 1300 degrees C, respectively. The phase relations also suggest that the natural chromitites in the Luobusa ophiolite previously interpreted as formed in the deep-mantle were formed at pressure below 12-16 GPa.

A polar LiNbO3-type (LN-type) titanate ZnTiO3 has been successfully synthesized using ilmenite-type (IL-type) ZnTiO3 under high pressure and high temperature. The first principles calculation indicates that LN-type ZnTiO3 is a metastable phase obtained by the transformation in the decompression process from the perovskite-type phase, which is stable at high pressure and high temperature. The Rietveld structural refinement using synchrotron powder X-ray diffraction data reveals that LN-type ZnTiO3 crystallizes into a hexagonal structure with a polar space group R3c and exhibits greater intradistortion of the TiO6 octahedron in LN-type ZnTiO3 than that of the SnO6 octahedron in LN-type ZnSnO3. The estimated spontaneous polarization (75 mu C/cm(2), 88 mu C/cm(2)) using the nominal charge and the Born effective charge (BEC) derived from density functional perturbation theory, respectively, are greater than those of ZnSnO3 (59 mu C/cm(2), 65 mu C/cm(2)), which is strongly attributed to the great displacement of Ti from the centrosymmetric position along the c-axis and the fact that the BEC of Ti (+6.1) is greater than that of Sn (+4.1). Furthermore, the spontaneous polarization of LN-type ZnTiO3 is greater than that of LiNbO3 (62 mu C/cm(2), 76 mu C/cm(2)), indicating that LN-type ZnTiO3, like LiNbO3, is a candidate ferroelectric material with high performance. The second harmonic generation (SHG) response of LN-type ZnTiO3 is 24 times greater than that of LN-type ZnSnO3. The findings indicate that the intraoctahedral distortion, spontaneous polarization, and the accompanying SHG response are caused by the stabilization of the polar LiNbO3-type structure and reinforced by the second-order Jahn-Teller effect attributable to the orbital interaction between oxygen ions and d(0) ions such as Ti4+.

We successfully prepared the perovskite-type lanthanum lithium titanate (LLTO) ceramics electrolytes with high total lithium ion conductivity of 3-5 x 10(-4) S cm(-1) at 300 K. The high total conductivity is attributed to the elimination of resistive grain boundary by the grain growth. Using the electrolyte as a separator, a rechargeable aqueous-type lithium/air cell which composed of Li metal/Li organic electrolytes/LLTO ceramics tube/LiOH aq/O-2 carbon electrodes was developed and the stable discharge/charge behaviors were confirmed. Owing to the low porosity and the stability to alkaline aqueous solution of LiOH as well as high ionic conductivity, the lithium ion-conducting lanthanum lithium titanate ceramics is suitable for an electrolyte separator for aqueous-type rechargeable lithium/air batteries. (c) 2012 Elsevier B.V. All rights reserved.

The dielectric properties of a polar LiNbO3-type ZnSnO3 synthesized under high-pressure have been investigated with respect to the dielectric permittivity in the relative low frequency range of 10 kHz to 1 MHz and the SHG response at an optical frequency. The small temperature dependence of dielectric permittivity without anomaly was observed in the temperature range of 300 K to 780 K. LiNbO3-type ZnSnO3 exhibits the maximum SHG efficiency of approximately 50 times that of quartz. We then compare the structure and SHG response with those of iso-structural LiNbO3 and other known LiNbO3-type oxides. It was found that the magnitude of SHG response is correlated to the magnitude of intra-octahedral distortion, which is effectively brought by the second-order Jahn-Teller effect. (C) 2012 Elsevier Inc. All rights reserved.

NaNiF3 perovskite was found to transform to post-perovskite at 16-18 GPa and 1273-1473 K. The equilibrium transition boundary is expressed as P (GPa)= -2.0+0.014 x T (K). Structure refinements indicated that NaNiF3 perovskite and post-perovskite have almost regular NiF6 octahedra consistent with absence of the first-order Jahn-Teller active ions. Both NaNiF3 perovskite and post-perovskite are insulators. The perovskite underwent a canted antiferromagnetic transition at 156 K, and the post-perovskite antiferromagnetic transition at 22 K. Magnetic exchange interaction of NaNiF3 post-perovskite is smaller than that of perovskite, reflecting larger distortion of Ni-F-Ni network and lower dimension of octahedral arrangement in post-perovskite than those in perovskite. (C) 2012 Elsevier Inc. All rights reserved.

New perovskite-type oxyfluoride, PbMnO2F was synthesized under 4-7 GPa at 1000 degrees C. As a result of X-ray and electron diffractions, the compound was determined to have tetragonal perovskite structure with a x a x 4c super structure where a and c are the lattice parameters of the perovskite subcell. The tetragonality, c/a, attained maximum, c/a = 1.100, for PbMnO2F synthesized under 4 GPa.

A polycrystalline perovskite CaTiO3:Pr-3+ was synthesized and the temperature dependence of luminescence properties was investigated in the temperature range of 6-440 K. CaTiO3:Pr3+ exhibits red emission ascribed to the f-f transition from the excited state D-1(2) to the ground state H-3(4) of Pr3+ upon the band gap photo-excitation between valence and conduction band, and upon the IVCT (inter valence charge transfer between Pr3+ and Ti4+) photo-excitation. Below 330K, the emission intensity upon the band gap excitation increased with temperature, while the temperature dependence of emission intensity upon the IVCT excitation is relatively small, indicating that the electron transfer process between Pr3+ and the host accompanied by the band gap excitation is thermally activated. Above 330 K. the thermal quenching of emission was observed upon both of the band gap and the IVCT excitation and the energy barrier for thermal quenching was estimated to be similar to 5500 cm(-1). (C) 2011 Elsevier B.V. All rights reserved.

A high-pressure phase of CaRhO3 stable between perovskite and post-perovskite in P-T space was synthesized at 17 GPa and 1650 degrees C using a multi-anvil apparatus. The crystal structure of CaRhO3 was solved by the structure prediction evolutionary algorithm and was refined by Rietveld analysis of the synchrotron powder X-ray diffraction pattern, along with transmission electron microscopy observations. The structure is monoclinic with lattice parameters of a = 12.5114(1) angstrom, b = 3.1241(1) angstrom, c= 8.8579(1) angstrom, beta = 103.951 (1)degrees, V= 336.01(1) angstrom(3) with space group P2(1)/m. The structure contains edge-sharing RhO6 octahedral chains along the b-axis. The six RhO6 octahedral chains make a unit, which stacks up alternatively with the CaO8 polyhedral layer along the [101] direction to form the structure of CaRhO3 intermediate phase.

We synthesized two high-pressure polymorphs PbNiO3 with different structures, a perovskite-type and a LiNbO3-type structure, and investigated their formation behavior, detailed structure, structural transformation, thermal stability, valence state of cations, and magnetic and electronic properties. A perovskite-type PbNiO3 synthesized at 800 degrees C under a pressure of 3 GPa crystallizes as an orthorhombic GdFeO3-type structure with a space group Pnma. The reaction under high pressure was monitored by an in situ energy dispersive X-ray diffraction experiment, which revealed that a perovskit-type phase was formed even at 400 degrees C under 3 GPa. The obtained perovskite-type phase irreversibly transforms to a LiNbO3-type phase with an acentric space group R3c by heat treatment at ambient pressure. The Rietveld structural refinement using synchrotron X-ray diffraction data and the XPS measurement for both the perovskite- and the LiNbO3-tyze phases reveal that both phases possess the valence state of Pb4+Ni2+O3. Perovskite-type PbNiO3 is the first example of the Pb4+M2+O3 series, and the first example of the perovskite containing a tetravalent A-site cation without lone pair electrons. The magnetic susceptibility measurement shows that the perovskite- and LiNbO3-type PbNiO3 undergo antiferromagnetic transition at 225 and 205 K, respectively. Both the perovskite- and LiNbO3-type phases exhibit semiconducting behavior.

Layered oxides, ruthenium-substituted Li2MnO3, were synthesized at 800 degrees C and 1200 degrees C. Their phase relation and electrical and electrochemical properties were investigated. Li2Mn1-xRuxO3 synthesized at 800 degrees C clearly separated into two phases, manganese-rich and ruthenium-rich phases, except for the narrow composition range of 0 <= x <= 0.05, while Li2Mn1-xAuxO3 synthesized at 1200 degrees C formed two solid solutions in the whole composition range across a structural transition between x=0.6 and 0.8. The electrical resistivity of Li2Mn1-xRuxO3 decreased with increasing ruthenium content. Li2Mn0.2RU0.8O3 (x = 0.8) synthesized at 1200 degrees C showed the lowest resistivity of 5.7 x 10(2) Omega cm at room temperature. The discharge capacity and cycling performance were improved by the ruthenium substitution. Li2Mn0.4Ru0.6O3 (x = 0.6) exhibited a discharge capacity of 192 mAh g(-1) in the initial cycle and 169 mAh g(-1) in the tenth cycle with high and almost constant charge-discharge efficiencies of 99% from the second to tenth cycle at a current rate of 1/10C. The ruthenium substitution to Li2MnO3 is quite effective to improve electrical conductivity and charge-discharge performance. (C) 2010 Elsevier B.V. All rights reserved.

LiNbO3-type MnMO3 (M = Ti, Sn) were synthesized under high pressure and temperature; their structures and magnetic, dielectric, and thermal properties were investigated; and their relationships were discussed. Optical second harmonic generation and synchrotron powder X-ray diffraction measurements revealed that both of the compounds possess a polar LiNbO3-type structure at room temperature. Weak ferromagnetism due to canted antiferromagnetic interaction was observed at 25 and 50 K for MnTiO3 and MnSnO3, respectively. Anomalies in the dielectric permittivity were observed at the weak ferromagnetic transition temperature for both the compounds, indicating the correlation between magnetic and dielectric properties. These results indicate that LiNbO3-type compounds with magnetic cations are new candidates for multiferroic materials.

We synthesized polycrystalline pristine and Pr3+-doped perovslcites La1/3MO3 (M = Nb, Ta):Pr3+ and investigated their crystal structure, optical absorption, and luminescence properties. The optical band gap of La1/3NbO3 (3.2 eV) is smaller than that of La1/3TaO3 (3.9 eV), which is primarily due to the difference in electronegativity between Nb and Ta. In La1/3NbO3: Pr3+, the red emission assigned to the f-f transition of Pr3+ from the excited D-1(2) level to the ground H-3(4) state upon band gap photoexcitation (near-UV) was observed, whereas the f-f transition of Pr3+ with blue-green emission from the excited P-3(o) level to the ground H-3(4) state was quenched. On the other hand, in La1/3TaO3:Pr3+, the blue-green emission upon band gap photoexcitation was observed. Their differences in emission behavior are attributed to the energy level of the ground and excited states of 4f(2) for Pr3+, relative to the energy levels of the conduction and valence bands, and the trapped electron state, which mediates the relaxation of electron from the conduction band to the excited state of Pr3+. La1/3NbO3:Pr3+ is a candidate red phosphor utilizing near-UV LED chips (e.g., lambda = 375 nin) as an excitation source.

A quasi-one-dimensional magnetism was discovered in the post-perovskite CaRuO3 (Ru4+: 4d(4), Cmcm), which is isocompositional with the perovskite CaRuO3 (Pbnm). An antiferromagnetic (AFM) spin-chain function with -J/k(B) = 350 K reproduces the experimental curve of the magnetic susceptibility vs temperature well, suggesting long-range AFM correlations. The anisotropic magnetism is probably owed to the d(yz)-2p(pi)-d(zx) and d(zx)-2p(pi)-d(yz) superexchange bonds along the a axis. The Sommerfeld coefficient of the specific heat is fairly small, 0.16(2) mJ mol(-1) K-2, indicating that the magnetism reflects the localized nature of the 4d electrons. This is an observation of an integer (S = 1) spin-chain AFM in the 4d electron system.

An A-site ordered perovskite oxide SrCu3Ti4O12 was synthesized under high pressure and temperature conditions. The sample was characterized by the synchrotron X-ray diffraction, dielectric and magnetic susceptibility measurements. The synchrotron X-ray Rietveld refinement revealed that the strontium ion fully occupied on the A-site, while the copper ion at the A'-site was slightly deficient. The dielectric constant was about 160 at 1 kHz at room temperature. The anti-ferromagnetic (AFM) order with a Neel-temperature T-N of at 24.5 K was observed. The ionic radii of the A-site ion had little influence on AFM indirect exchange interaction between Cu2+ ions in A Cu3Ti4O12.

The spectroscopic properties of R1/2Na1/2TiO3:Pr3+ (R=La, Gd, Y, Lu) are investigated in the temperature range 77-500 K and interpreted in the frame of the intervalence charge transfer (IVCT) model. The model allowed locating the ground state of Pr3+ relative to the host fundamental bands with an accuracy of 0.1-0.2 eV. (C) 2010 Elsevier B.V. All rights reserved.

A novel polar oxide of ZnSnO3 with LiNbO3-type structure has been investigated using first-principles density functional theory. The calculated pressure dependence of the phase stability in the ternary Zn2+-Sn4+-O2- system confirms the experimental results and detailed mechanism of the pressure-induced phase transition (see Fig.). High spontaneous polarization of 56.9 degrees C cm(-2) is calculated by the Berry-phase approach, and it is attributed to the large displacement of Zn2+ and its strong ionicity. Further improvement of the spontaneous polarization is suggested by enhancing the covalency of Sn4+ sites.

The predominant factors of the activation energy for ionic conductivity in perovskite-type lithium ion-conducting oxides were discussed in terms of structural distortion. As the result, the activation energies in almost all compounds are governed by a factor, a(p)/(B-large-O) (a(p) : perovskite parameter (cube root of cell volume per formula unit), (B-large-O) : inter-atomic distance between larger B ion and oxygen ion). This finding implies that (i) the larger B ion gives rise to structural distortion such as the tilt of the BO6 octahedra, which decrease the bottleneck size, (ii) the resultant smaller bottleneck determines the activation energies for ionic diffusion.

We found that two lithium niobate-type oxides, CdPbO(3) and PbNiO(3) were synthesized by high-pressure as metastable low-pressure perovskite-type phases. We then discussed the stability of lithium niobate-type and perovskite-type oxides relative to oxides with other structure for ABO(3) compounds. Consequently, the tolerance factor of perovskite is not the only predominant one to determine the stability and the crystal field effects of 3d transition metal ions are also important.

CaRuO3 post-perovskite which has quasi-two-dimensional lattice shows one dimensional antiferromagnetism such as Bonner-Fisher type above 400 K. The Neel temperature, T-N, is around 270 K.

We synthesized a perovskite-type oxynitride, LaTiO2N by nitridation of the oxide precursor under NH3 atmosphere it low temperature all flow rate. We successfully synthesized LaTiO2N at. 1023 K (750 degrees C) under flowing NH3 gas at a rate of 18 dm(3)/h using a handmade rotary furnace form tie amorphous oxide precursor prepared by a sol-gel technique-polymerizable complex method. The average particle size of tie LaTiO2N sample prepared at 1023 K (750 degrees C) (LTON-750) was smaller than for the LaTiO2N sample prepared by I conventional solid-state reaction method at 1223 K (950 degrees C) (LTON-SS). The smallest particle size of LTON-750 was estimated at 20-30 nm. The BET surface area of LTON-750, calculated front the N-2 adsorption isotherm. was 35.0 m(2)/g. This is approximately 2 fillies greater than that of LTON-SS. Furthermore, LTON-750 and LTON-SS demonstrated the ability to adsorb 11, at 77 K. (C) 2009 The Ceramic Society of Japan All rights reserved

High-resolution electron microscopy (HREM) and energy dispersive X-ray spectroscopy (EDS) studies of (La, M)TiO3 (M = Zn, Mn) prepared by M/Li ion exchange were performed to clarify the microscopic mechanism of ion-exchange reactions. At a macroscopic level, EDS analysis revealed that Zn and Mn atoms were homogeneously dispersed in matrix grains of (La, Zn)TiO3 and (La, Mn)TiO3 samples, respectively. EDS analysis also revealed that no segregation of Zn and Mn atoms was observed even in the vicinity of grain boundary regions. HREM and EDS analysis demonstrated that the microscopic mechanism of ion-exchange reactions was different by the ion-exchanged metals.

Perovskite thin-film electroluminescence devices are prepared, opening up a new optical application of perovskite materials. With increasing driving voltage, the intensity of electroluminescence increases dramatically. High-quality red color is produced and the working voltage for whole-surface electroluminescence is as low as 10 V.

We report that the orthorhombic-rhombohedral phase transition temperature in sodium potassium niobate could be tuned from lower to higher than room temperature by incorporating barium zirconate into it. It is revealed that when barium zirconate is between 8 mol% and 15 mol%, the solid solution exhibits rhombohedral symmetry at room temperature. Rietveld analysis shows that the space group of the rhombohedral phase is Ram. It is suggested that a relatively larger B-cation favors the low-temperature phase which is a common phenomenon for perovskite ferroelectrics. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The La ordering and domain structures of La(2/3 - x)Li(3x)TiO(3) single crystals and quenched samples have been observed by high resolution electron microscopy. in single crystals, the grown single crystals are not real single crystals with mono-domain, but crystals with 90 degrees oriented domains with 20-100 nm sizes. A remarkable difference of the domain size between polycrystals and single crystals has not been observed at the same composition. In quenched samples, the La disordering has been observed. Furthermore, domain structures of quenched samples are different from those of furnace-cooled ones. Domain structures change with the La disordering. The understanding of microstructures is necessary to clarify the Li-ion conduction mechanism. (C) 2008 Elsevier B.V. All rights reserved.

A high-quality polycrystalline sample of the correlated 4d post-perovskite CaRhO3 (Rh4+: 4d(5), S-el = 1/2) was attained under a moderate pressure of 6 GPa. Since the post-perovskite is quenchable at ambient pressure/temperature, it can be a valuable analogue of the post-perovskite MgSiO3 (stable higher than 120 GPa and unstable at ambient pressure), which is a significant key material in earth science. The sample was subjected for measurements of charge-transport and magnetic properties. The data clearly indicate it goes into an antiferromagnetically ordered state below similar to 90 K in an unusual way, in striking contrast to what was observed for the perovskite phase. The post-perovskite CaRhO3 offers future opportunities for correlated electrons science as well as earth science.

A novel perovskite, PbFe1/2V1/2O3 was successfully synthesized tinder 7 GPa. PbFe1/2V1/2O3 exhibits a highly distorted tetragonal perovskite structure (c/a = 1.18) with the disordered arrangement of Fe and V at room temperature. The XPS reveals that the oxidation states of each ion are Pb2+, Fe3+, and V5+, respectively. The large tetragonal distortion is related to not only the presence of Pb2+ ion but also V5+ with an electronic configuration of d(0). No structural phase transition up to 490 K above room temperature was observed by a high-temperature X-ray diffraction experiment. The temperature dependence of magnetic susceptibility exhibits non-Curie-Weiss behavior, which is attributed to the antiferromagnetic interaction between Fe3+-O2--Fe3+ originated from the disordered arrangement of Fe3+ and V5+ ions. (C)2009 The Ceramic society of Japan. All rights reserved.

La0.61Li0.17TiO3 microstructures have been studied by high resolution electron microscopy. A local lattice distortion occurs in the vicinity of the domain boundary region due to the twin with an angle of 89. The average domain size of La0.61Li0.17TiO3 is greater than 20 nm. The domain size and structures of La0.61Li0.17TiO3 differ greatly from those of La-poor compounds, such as La0.55Li0.35TiO3. At a nanoscopic level, microdomains of 20-100 nm in size construct a two-dimensional structure in La-rich compounds, while microdomains of 5-10 nm in size construct a three-dimensional structure in La-poor compounds. In addition, the Li-ion conduction mechanisms for La-rich and La-poor compounds are two- and three-dimensional, respectively.

We synthesized a novel perovskite-type oxyfluoride, PbScO2F, and investigated its crystal structure, thermal stability and dielectric properties. PbScO2F has a Cubic perovskite-type structure With Pb ions displaced from the ideal A-site positions along the < 110 > direction. By thermal gravity and differential thermal analyses, we found that this compound is stable up to 963 K (690 C) under ambient atmosphere. The dielectric permittivity of PbScO2F is approximately 80, at room temperature, which is almost the same as KTiO2F and smaller than that of PbFeO2F. Furthermore, an anomaly in the dielectric permittivity was observed in the vicinity of 100K that seems to be related to the displacement of the Pb ions. (C) 2008 Published by Elsevier Inc.

We investigated the lattice parameters and luminescent properties of Pr-doped perovskite-type lithium ion conductors with the nominal composition, A(0.6-3x/2)Pr(x)Li(0.3)Ti(0.5)Ta(0.5)O(3) (A =Ca and Sr, 0 <= x <= 0.05). Ca0.6Li0.3Ti0.5Ta0.5O3: Pr showed the intense red emission corresponding to the f-f transition of Pr3+ (D-1(2)-> H-3(4)) on the ultraviolet photo excitation with the energy corresponding to the band gap of host. In contrast, Sr0.6Li0.3Ti0.5Ta0.5O3: Pr exhibited blue-green and red emission on the excitation with blue light corresponding to the f-f transition of pr(3+) (H-3(4)-> P-3(2))- It was found that these differences in luminescent properties primarily originate from the occupation site of Pr in these perovskite-type oxides. (C) 2007 Elsevier B.V. All rights reserved.

We synthesized xKTiO(2)F-(1-x)BaTiO3 solid solution by the high pressure and temperature method. With regard to the temperature dependence of the dielectric permittivity, the three anomalies corresponding to the three phase transitions of BaTiO3 merged with the increase in x, and only one peak was observed for 0.12 <= x <= 0.20. The variation in T-C with the composition, dT(C)/d(x), of xKTiO(2)F-(1-x)BaTiO3 was approximately -14 K/mol % for x >= 0.12, which is almost the same as and larger than that of the 1/3xBaLiF(3)-(1-1/3x)BaTiO3 and Ba(Ti1-xMx)O-3 (B=Zr, Sn, Hf, and Ce) solid solutions, respectively. This result indicates that the phase transition temperature is significantly affected by the substitution with F ion. Furthermore, it was found that the 0.15KTiO(2)F-0.85BaTiO(3) is an ideal relaxor and that the remnant polarization is 5.6 mu C/cm(2) at 70 K. which is comparable to that of Ba(Ti0.7Zr0.3)O-3. However, the epsilon(m) of 0.15KTiO(2)F -0.85BaTiO(3) (approximate to 5000 at 100 kHz) was smaller than that of the B-site ion-substituted relaxors: Ba(Ti0.7Zr0.3)O-3 and Ba(Ti0.82Sn0.18)O-3. Since the remnant polarization of 0.15KTiO(2)F -0.85BaTiO(3) at 70 K was comparable to that of Ba(Ti0.7Zr0.3)O-3 at 175 K, the small epsilon(m) of 0.15KTiO(2)F-0.85BaTiO(3) is found to be due to the decrease in the dielectric permittivity in the paraelectric region. (C) 2008 American Institute of Physics.

We synthesized a novel perovskite-type oxide, HgSnO3, under high pressure and high temperature, and investigated the crystal and electronic structures as well as the transport properties. It was found that HgSnO3 possesses a trigonal-hexagonal lattice with space group R (3) over barc. The band gap of HgSnO3 estimated by diffuse reflectance spectrum measurement is relatively small (1.6 eV), irrespective of the large octahedral tilting distortion. The small band gap is caused by the increase in the bandwidth of the conduction and valence bands due to mixing between the empty Hg 6s orbitals and the antibonding Sn 5s-O 2p states and the mixing between the filled Hg 5d orbitals and the O 2p states, respectively. The electronic resistivity, Seebeck coefficient, and Hall coefficient measurements indicate that as-synthesized HgSnO3 is an n-type semiconductor.

A polar oxide ZnSnO3 was synthesized by a solid-state reaction under a pressure of 7 GPa and a temperature of 1000 degrees C. The crystal structure was determined by Rietveld analysis of the X-ray powder diffraction data. ZnSnO3 has a rhombohedral LiNbO3-type structure with unit cell parameters, a = 0.52622(1) nm, c = 1.40026(2) nm (space group: R3c). The polar structure is characterized by the large displacement of Zn along the c-axis in the ZnO6 octahedron based on the strong chemical bonding between Zn and three O. ZnSnO3 is a candidate piezoelectric and pyroelectric material as well as nonlinear optical material.

A new ternary platinum oxide, CaPtO3 was synthesized under a pressure of 7 GPa and a temperature of 1000 degrees C. The crystal structure of CaPtO3 was determined by Rietveld analysis of the X-ray powder diffraction data. CaPtO3 has a layered CalrO(3)-type structure (orthorhombic, space group: Cmcm), which is the same as that of a post-perovskite MgSiO3 in the Earth's lower mantle. The magnetic susceptibility data indicate that the Pt ion in CaPtO3 is tetravalent in the low spin state with an electron configuration of t(2g)(6)e(g)(0) (S = 0). This finding is consistent with the insulating behavior.

Pr3+-doped perovskites R1/2Na1/2TiO3:Pr (R = La, Gd, Lu, and Y) were synthesized, and their structures, optical absorption and luminescent properties were investigated, and the relationship between structures and optical properties are discussed. Optical band gap of R1/2Na1/2TiO3 increases in the order R = La, Gd, Y, and Lu, which is primarily due to a decrease in band width accompanied by a decrease in Ti-O-Ti bond angle. Intense red emission assigned to f-f transition of Pr3+ from the excited D-1(2) level to the ground H-3(4) state upon the band gap photo-excitation (UV) was observed for all compounds. The wavelength of emission peaks was red-shifted in the order R = La, Gd, Y, and Lu, which originates from the increase in crystal field splitting of Pr3+. This is attributed to the decrease in inter-atomic distances of Pr 0 together with the inter-atomic distances (R, Na)-O, i.e., increase in covalency between Pr and O. The results indicate that the luminescent properties in R1/2Na1/2TiO3:Pr are governed by the relative energy level between the ground and excited state of 4f(2) for Pr3+, and the conduction and valence band, which is primarily dependent on the structure, e.g., the tilt of TiO6 octahedra and the Pr-Ti inter-atomic distance and the site symmetry of Pr ion. (c) 2007 Elsevier Inc. All rights reserved.

Nano-scale structural analysis of (La, Fe)TiO3 prepared by Fe/Li ion-exchange has been performed by high resolution transmission electron microscopy and analytical electron microscopy. An ion-exchange reaction has been microscopically confirmed. On the other hand, the nanocrystalline bcc-Fe phase segregates as a secondary phase at grain boundaries. Interfaces between grain boundaries and matrix grains of (La, Fe)TiO3 maintain the coherency. The bcc-Fe phase at the grain boundaries may be the origin of the ferromagnetic behavior in (La, Fe)TiO3. (C) 2007 Elsevier Ltd. All rights reserved.

Lithium ion-conducting perovskite-type oxides, e.g., La2/3-xLi3TiO3 show high ionic conductivities as high as 10(-5)-10(-1) Scm(-1) at room temperature. Their high conductivities are attributed to the percolation-controlled diffusion of lithium ions via vacancies in the A-site-deficient perovskites (general formula of perovskite-type oxide: ABO(3)). The strong correlation between structure and percolation-controlled diffusion in the perovskites is primarily referred to the arrangement of A-site ions, and the "bottleneck" square-surrounded by four oxygen ions. The bottleneck size, i.e., the repulsion for lithium ions by the electronic clouds of oxygen ions, is dependent on the distortion and tilt of the BO6 octahedra, which relate to the difference of skeletal ions, A and B cations, i.e., tolerance factor and their chemical characters, and is the predominant factor of the activation energy for ion migration. These findings were confirmed by powder X-ray and neutron structural refinements, composition, temperature and hydrostatic pressure dependences of ionic conductivities, and molecular dynamics simulations.

The average structure and microstructure of a lithium-ion conducting perovskite La2/3-xLi3xTiO3 (x = 0.12) were investigated using neutron diffraction and transmission electron microscopy (TEM). The obtained results were compared with those of previous studies on La2/3-xLi3xTiO3 series compounds, and the relationship between their structures and ionic conduction was discussed. The Rielveld refinement using neutron diffraction data reveals that the average structure (space group: Cmmm) of furnace-cooled Li-rich La2/3-xLi3-xTiO3 (x=0.12) involves alternative ordered arrangement of La along the c-axis and anti-phase-tilt of TiO6 octahedra along the b-axis as with Li-poor La2/3-xLi3-xTiO3(x=0.05). It was found that the strong correlation between structure and percolative diffusion pathways in the perovskites is primarily referred to the ordered arrangement of La ions, and the "bottleneck" square-surrounded by four oxygen ions determined by the distortion and tilt of TiO6 octahedra. In addition, the 90 degrees-oriented micro-domain structure, which also influences the percolative diffusion pathways in La2/3-xLi3xTiO3, was observed by TEM. (c) 2006 Elsevier B.V. All rights reserved.

Lithium ions of perovskite-type lithium ion conductor La0.55Li0.35TiO3 were replaced by divalent Mg2+ Zn2+, and Mn2+ ions in an ion exchange reaction using molten chlorides. The polycrystalline Mg-exchanged and Zn-exchanged samples are solid electrolytes for divalent Mg2+ and Zn2+ ions, whose dc ionic conductivities (sigma = 2.0 x 10(-6) S cm(-1) at 558 K for the Mg-exchanged sample, La-0.56(2)Li0.02(1)Mg0.16(1)TiO3.01(2) and sigma = 1.7 x 10(-6) S cm(-1) at 708 K for the Zn-exchanged samples, La0.55(1)Li0.0037(2)Zn0.15(1)TiO2.98(2)) were compared to those of the known highest Mg2+ and Zn2+ inorganic solid electrolytes. The Mn-exchanged sample, then, showed paramagnetic behavior in the temperature range of 2 to 300 K. The Mn ions in the exchanged sample are divalent and the spin configuration is in high spin state (S=5/2). (c) 2006 Elsevier B.V. All rights reserved.

The perovskites PbFeO2F and 0.5PbFeO2F-0.5PbTiO 3 were synthesized at high temperatures (1000 °C) and high pressures (4-6 GPa). The crystal and magnetic structures were determined using powder neutron diffraction. Quenched PbFeO2F has the cubic perovskite-type, Pm3m, structure in which the Pb ion shifts from ideal A-site along the &lt 110&gt directions, which is in good accordance with a previous report. The magnetic structure is anti ferromagnetic G-type with propagation vector * = (1/2 1/2 1/2) and an Fe3+ ordered moment of 3.83 μB at 283K. The Néel temperature is 655(5) K. Annealed PbFeO2F has a tetragonal perovskite-type structure at room temperature and transforms reversibly from tetragonal to cubic at approximately 470 K. A superlattice with dimensions a × a × 5c is observed both in electron and x-ray diffraction. The solid solution 0.5PbFeO2F-0. 5PbTiO3 belongs to the non-centrosymmetric space group P4mm. The magnetic structure is G-type anti ferromagnetic and shows a weak ferromagnetic moment at 4 K. Consequently, 0.5PbFeO2F-0.5PbTiO3 is simultaneously ferroelectric and a weak ferromagnet at low temperature. The Nèel temperature is 450 K but the temperature dependence of the ordered Fe moment is anomalous. © 2007 Materials Research Society.