Shuki Torii

Structural and piezoelectric properties of high-density (Bi0.5K0.5)TiO3-BiFeO3 ceramics

The crystal structures and dielectric, polarization, and piezoelectric properties of high-density x(Bi0.5K0.5)TiO3–(1−x)BiFeO3 ceramics were investigated. The results obtained using x-ray and neutron powder diffractions and transmission electron microscopy showed that a morphotropic phase boundary between the rhombohedral (ferroelectric) and pseudocubic (ferroelectric) phases is present in 0.4<x<0.43. Ceramics with x=0.4 exhibited a large remanent polarization of 52 μC/cm2 at 25 °C and their piezoelectric properties were maintained up to 300 °C. It is suggested that the presence of nanosized domains with a polar rhombohedral structure observed for x=0.4 is the origin of relaxor-like dielectric properties.

Real-time observations of lithium battery reactions—operando neutron diffraction analysis during practical operation

Among the energy storage devices for applications in electric vehicles and stationary uses, lithium batteries typically deliver high performance. However, there is still a missing link between the engineering developments for large-scale batteries and the fundamental science of each battery component. Elucidating reaction mechanisms under practical operation is crucial for future battery technology. Here, we report an operando diffraction technique that uses high-intensity neutrons to detect reactions in non-equilibrium states driven by high-current operation in commercial 18650 cells. The experimental system comprising a time-of-flight diffractometer with automated Rietveld analysis was developed to collect and analyse diffraction data produced by sequential charge and discharge processes. Furthermore, observations under high current drain revealed inhomogeneous reactions, a structural relaxation after discharge, and a shift in the lithium concentration ranges with cycling in the electrode matrix. The technique provides valuable information required for the development of advanced batteries.

Powder neutron diffraction study of Ln-substituted PbWO4 oxide ion conductors

Abstract Structure refinements have been carried out on pure and lanthanide-substituted PbWO4 using powder neutron diffraction, and the defect structures of La- and Pr-substituted PbWO4 are discussed. The Rietveld refinement structure of pure PbWO4 agreed well with previous results. In the Pb1−xLaxWO4+x/2 system, the oxide ion interstitials seemed to be rather localized around z=0.3 of the 8e position (0 0 z) or the adjacent general position of the scheelite structure-type with I41/a symmetry. The deduced interstitial position is considered in terms of the oxide ion conduction path. A similar defect structure has been determined for the praseodymium-substituted compound, Pb1−xPrxWO4+x/2. In contrast, Pb1−xLa2x/3WO4-type substitution resulted in the formation of a cation-deficient structure.

Development of SPICA, New Dedicated Neutron Powder Diffractometer for Battery Studies

SPICA, a new special environment powder neutron diffractometer was built at BL09 in the Material and Life science Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC). This is the first instrument dedicated solely to the study of next-generation batteries in J-PARC and is optimized for in situ measurements to clarify structural changes of materials in batteries. The basic design and instrumentation of SPICA have been completed. The highest Δd/d resolution achieved at the commissioning stage was 0.09% at the back scattering bank of SPICA. The reliability of the diffraction data has achieved a sufficiently high level for the structural analysis of materials using the Rietveld method. The air scattering banks with the blades made of B4C for in situ measurements also function very well.

Structural and Magnetic Phase Determination of (1-x)BiFeO3–xBaTiO3 Solid Solution

Solid solutions of (1- x )BiFeO 3 – x BaTiO 3 ( x = 0.0–1.0) were studied by the combination of X-ray and neutron powder diffraction methods in order to investigate structural and magnetic properties over a wide temperature region. The structure analyses revealed that there exists a hexagonal phase over the wide range of x , and a coexistence of a cubic or a tetragonal phase was revealed. The compositions of the two coexisting phases differ from each other, and Ba and Ti were found to favor the cubic or tetragonal phase. As x increases, the relaxation of the rhombohedral distortion in the hexagonal phase was observed. The decreases of the ferroelectric and the antiferromagnetic phase transition temperatures were also observed leading the suppression of the polarization and the magnetic moment of Fe 3+ ion at room temperature. As a whole, the ferroelectricity and ferromagnetism in this material were considered to arise from the remaining hexagonal phase.

A-Site and B-Site Charge Orderings in an s–d Level Controlled Perovskite Oxide PbCoO3

Perovskite PbCoO3 synthesized at 12 GPa was found to have an unusual charge distribution of Pb2+Pb4+3Co2+2Co3+2O12 with charge orderings in both the A and B sites of perovskite ABO3. 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+Pb4+3Co2+2Co3+2O12 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.

High-temperature phase transition in lanthanum titanate perovskite La0.64(Ti0.92,Nb0.08)O3

Abstract High-temperature phase transition of lanthanum niobium titanate La 0.64 (Ti 0.92 ,Nb 0.08 )O 3 has been studied using neutron powder diffraction and the Rietveld method. The material is orthorhombic ( Cmmm ) between 295 and 534 K, while it is tetragonal ( P 4/ mmm ) between 637 and 740 K. The anti-phase tilt along the b axis of the oxygen octahedron around Ti and Nb atoms was found to induce the tetragonal-to-orthorhombic phase transition. The angle of the tilt and the b / a ratio of cell parameters decrease with an increase of temperature and become 0° and unity, respectively, at a transition temperature between 534 and 637 K.

Ordering of Oxygen and Nitrogen in J-Phase Lu4Si2O7N2

The crystal structure of cuspidine-type Lu 4Si2O7N2, the so-called J-phase, has been refined by Rietveld analysis from time-of-flight neutron powder diffraction data in order to confirm the ordering of oxygen and nitrogen atoms. This compound crystal lizes in a monoclinic cell, space group P21/c (No. 14-1) with a = 7.4243(1), b = 10.2728(1), c = 10.6628(1) Å, and β = 109.773(1)°. The diffraction peaks are also indexable with monoclinic lattice parameters of a = 7.4243(1), b = 10.2728(1), c = 10.7356(1) Å, and β = 110.828(1)°, space group P21/n (No. 14-2). The nitrogen atoms in Lu 4Si2O7N2 are connected to Si atoms and form Si 2(O,N)7 silicon oxynitride unit of composition Si 2O5N2. One N atom occupies the bridging site between Si atoms, and the other N atom is statisti c lly situated at the terminal sites. It is estimated that this unit comprises SiO 3N and SiO2N2 tetrahedra. The four Lu sites correspond to 6-fold, 7-fold (x2) and 8-fold coordination with Lu-(O,N) interatom ic distances of less than 2.9 Å. Introduction One of the interests in M–Si–O–N compounds is the configuration of oxyge n and nitrogen (O/N) in the structures. A cuspidine-type silicon-oxynitride with a general formula of RE4Si2O7N2 (RE = rare earth), the so-called RE-J-phase, has been known in sys tem of the type Si 3N4-SiO2-RE2O3 [1-9]. Recently, it has been found that Si 3N4 ceramics can have improved bending strength at high-temperatures by using Lu 2O3 as the additive instead of others such as Sc 2O3, La2O3, and Yb2O3 [10]. In Lu2O3-doped sintered Si 3N4 ceramics, the LuJ-phase, Lu 4Si2O7N2, was found at the grain boundary [11]. Unfortunately, only the cell constants and X-ray intensity data have been reported for Lu-J-phase [ 12]. The structure of LuJ-phase with respect to O/N configuration has not been investigated by other researc her . It is difficult to detect and distinguish light elements such as O and N by X-ray Key Engineering Materials Online: 2003-04-15 ISSN: 1662-9795, Vol. 237, pp 53-58 doi:10.4028/www.scientific.net/KEM.237.53

Hole-doping-induced melting of spin-state ordering in PrBaCo2O5.5+x

The layered perovskite cobaltite RBaCo

Crystal and Magnetic Structures of La2CoPtO6 Double Perovskite

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