Koya Hayashi

Crystal structures of La3Li5M2O12 (M=Nb, Ta)

Abstract Crystal structures of La 3 Li 5 M 2 O 12 (M=Nb, Ta) have been determined by a single crystal X-ray diffraction technique. La 3 Li 5 M 2 O 12 (M=Nb, Ta) has three dimensional framework structure consisting of La, Nb (Ta), O. The lithium atoms occupy two kinds of interstices in the framework, undistorted and distorted octahedral sites. The distorted octahedral sites are partially occupied by the lithium atoms. The non-stoichiometry of lithium and oxygen in La 3 Li 5 M 2 O 12 (M=Nb, Ta) is discussed.

Proton NMR in degraded powder of YBa2Cu3O7−δ

Pulsed NMR of 1H has been applied to characterize aged powders of YBa2Cu3O7-δ and its family. A proton site with an internal field of 150 Oe, which is from antiferromagnetically ordered copper moments, has been observed in antiferromagnetic, tetragonal Yba2Cu3O7-δ. A proton signal inside the superconducting region of orthorhombic YBa2Cu3O7-δ has been observed together with signals from regions of nonmagnetic, nonsuperconducting degraded products for both cases. Overall features are interpreted along with a recently proposed topotactic mechanism of hydration reaction.

New phases in La2O3Li2OTa2O5 system

A part of the phase diagram for the three-component system La/sub 2/O/sub 3/Li/sub 2/O-Ta/sub 2/O/sub 5/ was determined. Two new phases were found in the system. La/sub 3/Li/sub 7/Ta/sub 2/O/sub 13/ has a cubic lattice with space group Ia3d. La/sub 2/LiTaO/sub 6/ is the ordered pseudo-orthorhombic perovskite. These phases share phase boundaries with most phases of the ternary system.

Preparation and vibrational spectra of La2LiMO6 (M=Nb, Ta, Mo, Re, Ru, Os, and Ir)

Abstract Ordered orthorhombic perovskites, La2LiMo6(M=Nb, Ta, Mo, Re, Ru, Os, and Ir) were prepared. MO bond distances and MOM bond angles were estimated. Infrared and Raman spectra were observed. The correlation between vibrational frequencies and MO bond distances was discussed.

Phase relations and some electrical properties of compounds in TiS2-NbS2 system

The phase relations of the TiS{sub 2}-NbS{sub 2} system have been studied in the temperature range from 500 to 1,100 C. Three polytypes, 1T, 2H{sub a}, and 3R, are observed. The 1T-polytype is a high temperature phase, the 2H{sub a}-polytype is a medium temperature phase, and the 3R-polytype is a low temperature phase. The 1T-polytype spreads over almost the whole composition range of the system. The 2H{sub a}-polytype has a very narrow homogeneity range around 100% NbS{sub 2}. The 3R-polytype is stable in the composition range between 100% and 96% NbS{sub 2}. The electrical resistivity has been measured from 30 to 300 K. The magnetic susceptibility has been measured from 5 to 300 K. The samples of the 1T-Ti{sub 1{minus}x}Nb{sub x}S{sub 2} (X {le} 0.90) show the semiconductive behavior caused by an impurity scattering mechanism.

New phase in the La2O3-Li2O-Nb2O5 system

Abstract A part of the phase diagram for the three component system La 2 O 3 -Li 2 O-Nb 2 O 5 was determined. In this system, a new phase La 3 Li 7 Nb 2 O 13 was obtained. The crystal data of this phase are as follows: Space group: Ia3d; Lattice constant: a=12.96A; Density: 5.45g/cm 3 z=8.

Formation of TaSe2 polytypes and hydrogen impurity

Abstract Stability of TaS 2 polytypes is investigated. A small amount of hydrogen impurity stabilizes the trigonal prismatic coordination polytype. Especially the mixed coordination polytype is observed only with hydrogen impurity. The preparation of TaS 2 polytypes is systematized by considering the hydrogen impurity.

Thermoluminescence dating of the Ryukyu Limestone

Abstract Thermoluminescence [TL] dating of calcite is useful for corals in the Pleistocene Ryukyu Limestone in Okinawa Island, in which no aragonite is found. Fossil calcite corals in the Ryukyu Limestone have a variety of induced TL glow curves with peaks at about 150, 210, 250 and 310°C. The TL growth of a group of them exhibits supralinear behavior, while that of another group exhibits saturation behavior. Almost all of the TL ages of the corals which show the supralinear behavior are roughly consistent with ages estimated from geology and uranium-series and ESR ages.

Separation and Characterization of Superconducting YBa2Cu3O7-x Powder

The superconducting YBa2Cu3O7-x powder has been sorted using the Meissner effect. Two separation methods have been employed. One is separating the powder at a constant temperature, the other is separating it over a temperature gradient. Both methods are effective for separating the high-Tc superconducting powder from the low-Tc superconducting parts. Separated powder was examined by X-ray diffraction and quantitatively analyzed by EPMA as well as by chemical analysis, and by a TEM. The higher-Tc part of YBa2Cu3O7-x powder was characterized by smaller lattice constants, higher oxygen concentration, and higher twin density. The low-Tc YBa2Cu3O7-x sample shows a low Cu/Y ratio relative to the high-Tc sample.

Characterization of the layered transition-metal dichalcogenides with octahedral coordination

The lattice constants of nonstoichiometric CdI2-type transition-metal dichalcogenides exhibit a characteristic feature. One of the body-diagonal lengths of the hexagonal lattice is kept nearly constant over the homogeneity range. This body-diagonal direction involves the full-layer metal-chalcogen bonds. The heats of formation of various CdI2-type transition-metal dichalcogenides are correlated to the reduced length which is derived from that body-diagonal and the ideal ionic radii. The ΔHof values of the CdI2-type transition-metal dichalcogenides can be estimated from the following empilical formula within the error of about 10kcal/mole. ΔHof = 1030 LR − 144 (kcal/mole). LR: Reduced length.