Hideshi Fujishita

Crystal Structure Determination of Antiferroelectric PbZrO3 –Application of Profile Analysis Method to Powder Method of X-ray and Neutron Diffraction–

Crystal structure of antiferroelectric PbZrO 3 has been studied at room temperature by adopting X-ray and neutron profile analysis methods. A considerable refinement of the structure has been made on a previous model which has generally been accepted in these 20 years. In contrast to the old model which has a large spontaneous polarization, present model has no polarization at all, and the interatomic distances are reasonable magnitude. Several contradictions having been noticed between the dielectric properties and the structural nature are now completely resolved.

Comparison of the normal state properties between the superconducting and the nonsuperconducting metallic phases in La2−ySryCu−xNixO4

Abstract Structural, transport and magnetic properties have been studied for La2−ySryCu1−xNixO4 with varying x for several fixed y-values of 0.1, 0.15, 0.22, 0.32 and 0.45. For x=0, the superconductivity appears, as is already known, in the region of y c ⋍ 0.3 . For every value of y studied here, xc is defined as the concentration of x where the resistivity upturn with decreasing T becomes appreciable due to the electron localization. For y yc) phases are not largely different from each other.

Crystal Structure and Order Parameters in the Phase Transition of Antiferroelectric PbZrO3

X-ray and neutron diffraction and dielectric measurements were performed for the antiferroelectric phase of PbZrO 3 . The antiferroelectric Σ 3 (TO) and the R 25 superlattice-reflection intensities, and the pseudo-tetragonal lattice distortion of the perovskite sublattice showed the same temperature dependence below room temperature, showing a saturation below about 60 K. Above room temperature, however, they showed rather different temperature dependences. These temperature dependences can be well described by the free energy based on a group theoretical method, which includes a quantum effect. The atomic shifts do not necessarily conform to a simple concept of order parameter in soft mode condensation. However the antiferroelectric phase transition can be understood by the phenomenological theory for coupled order parameters if applied over the whole temperature region.

Neutron Scattering Study on Distribution of Cations in α-AgI-Type Superionic Conductors

Neutron diffuse scattering from powder samples of α-AgI type superionic conductors AgI, Ag 3 SI and Ag 2 S was measured using a triple-axis spectrometer with a fixed position of the energy analyzer so as to measure only the elastic scattering caused by a disordered distribution of cations. The disorder scattering curves thus obtained were analyzed under the assumption that Ag atoms distribute over crystallographic 12(d) sites among the bcc lattice formed by anions, and probability functions α n for a simultaneous occupation in the n-th neighbor sites were obtained. The results are discussed comparing with the pair correlation function g Ag–Ag ( r ) being obtained theoretically as well as by the analysis of X-ray diffuse scattering based on a liquid-like distribution model. The liquid phase of AgI was also studied by the same neutron technique and the results are discussed together with those for the solid phase.

Two-Dimensional Spin Correlation in YFe2O4

Neutron and X-ray diffraction studies were carried out on polycrystalline specimens of stoichiometric (S-) and non-stoichiometric (N-) YFe 2 O 4 . An asymmetric diffraction line was observed above the Neel point ( T N ≃235 K) in S-YFe 2 O 4 and both above and below T N ( T N ≃210 K) in N-YFe 2 O 4 . At above T N , the line profile was quantitatively interpreted as due to two-dimensional critical scattering, on an assumption that the scattering cross section is a Lorentzian in a h - k plane, independent of l . The correlation length, κ, and the susceptibility at (1/3, 1/3, l ), χ, obey an exponential law: κ∝( T - T N ′ ) v and χ∝( T - T N ′ ) -γ , respectively, with ν=1.5 ±0.05, γ=3.1 ±0.1 and T N ′ =233.0 ±0.5 K in S-YFe 2 O 4 . It was concluded that the spin correlation is two-dimensional in the hexagonal YFe 2 O 4 , both in the S- and N-compounds, but a crystal deformation induces a three-dimensional spin ordering in S-YFe 2 O 4 .

Re-Examination of the Antiferroelectric Structure of PbZrO3.

The crystal structure of antiferroelectric PbZrO 3 was re-examined by high resolution powder neutron diffraction. The structure obtained with assumed modulations associated with the lattice vibrational modes Σ 3 ( T O ) and R 25 x y is almost the same as that obtained previously with the same assumptions. However, one coordinate of oxygen positions obtained by the refinement for all crystallographically possible parameters is different from that obtained previously under the same conditions. The difference between the two sets of the structural parameters obtained here is meaningful. The result indicates that the modulation associated with the R 25 x y mode is fairly distorted. This structure agrees well with that recently investigated using local-density calculations.

X-Ray Crystal Structure Analysis of Low Temperature Phase of SrTiO3

The crystal structure analysis of the low temperature phase of SrTiO 3 has been made at 77 K using the method of X-ray oscillation photograph. The space group is determined as I4/mcm and the rotational shift of oxygen octahedra with respect to Sr ion frame is by 1.6°; this is slightly larger than those estimated from a previous ESR experiment, neutron diffraction study and from X-ray lattice parameter measurement. Observed temperature parameters are in reasonable agreement with previously reported ones estimated from a rigid shell model.

Anomalous thermoelectric power of Bi1.6Pb0.5Sr1.9-yLayCu1.05Oz

Abstract Thermoelectric power S of Bi1.6Pb0.5Sr1.9−yLayCu1.05Oz have been studied, where as a result of the La doping, the carrier concentration decreases and the system changes from normal metallic state for y∼0 to semiconducting one for y≳0.8 through superconducting phase. S of semiconducting samples is positive and large as in the case of similar samples of other Cu-oxides. A new surprising result is that the samples with y∼-0 exhibit rather large negative values of S at high temperatures, which has not been observed in other Cu-oxides in the nonsuperconducting metallic region with an overdoped carrier concentration. For the metallic samples, S is roughly divided into two contributions: One is linear in temperature T and has a negative slope and another is nearly constant above 100∼150K and decreases with decreasing T in low temperature region. The latter term suggests an existence of unusual scattering of carriers of Cu-oxygen.

Variation of Physical Properties of Bi1.6Pb0.5Sr1.9- yLa yCu1.05O z with the La-Concentration y across the Superconducting-Nonsuperconducting Metal Boundary

Experimental results on the variation of various physical properties in Bi 1.6 Pb 0.5 Sr 1.9- y La y Cu 1.05 O z with varying y through the superconducting and nonsuperconducting metallic phase boundary are presented. The magnetic susceptibility at fixed temperatures is monotonous functions of y . The Hall coefficient does not indicate even a weak tendency of the sign change at the boundary. The thermoelectric power has a systematic change with y and exhibits quite unusual behavior even in the nonsuperconducting metallic phase.

Propagating Collective Excitations in Liquid Bismuth

Neutron scattering measurements of the dynamical structure factor S ( Q , ω) of liquid Bi were carried out at 673 K in the range of the momentum transfer Q from 0.6 to 1.6 A -1 . Side peaks with the transfer energy less than about 8 meV were found in the S ( Q , ω) curves for \(Q \leqslant 1.2\) A -1 . They show a well defined dispersion curve which is connected with the dispersion line for small Q determined from the sound velocity. This indicates that the propagating collective excitations exist up to a relatively large momentum region even in the non-simple liquid metal as Bi.