Nobuyuki Yamamoto

Crystal structure and physical properties of layered perovskite compound Sr3V2O7.01

A layered perovskite compound Sr3V2O7.01 was synthesized by heating mixtures of the constituent oxides at 1110°C in flowing hydrogen atmosphere. Rietveld analysis based on powder X-ray diffraction data shows that the compound has a tetragonal structure (I4/mmm) with a = 3.8331(7) A and c = 20.2459(6) A. The resistivity of the compound is 4.8 mΩ· cm at room temperature (300 K) and decreases with decreasing temperature down to 2 K. The magnetic susceptibility can be represented by a summation of temperature-independent and Curie-Weiss terms. The effective number of Bohr magnetons per vanadium atom is 0.37, which is considerably smaller than the free-ion value of 1.73 for V4+.

Crystal structure and physical properties of a new layered perovskite compound Sr4V3O9.60

Abstract A new compound Sr4V3O9.60±0.01 has been synthesized by solid state reaction in flowing hydrogen atmosphere. Rietveld analysis based on X-ray diffraction data shows that it has a tetragonal structure (I4/mmm) with a = 3.8457(1) A and c = 27.9017(3) A . The resistivity of the compound is 1.4 mΩ · cm at room temperature (300 K) and decreases with decreasing temperature down to about 100 K followed by a slight increase with a further decrease of temperature. The magnetic susceptibility can be represented by a summation of temperature-independent and Curie-Weiss terms. The effective number of Bohr magnetons per vanadium atom is 0.37, which is considerably smaller than the free-ion values of 2.83 for V3+ and 1.73 for V4+. These results suggest that electron-electron interactions among the narrow π∗ band (t2g symmetry) electrons are important in this compound.

Electrical and magnetic properties of oxygen deficient layered perovskite Sr2VO4−δ with δ=0.18, 0.29, 0.38

Abstract The effect of the oxygen deficiency δ on the electrical and magnetic properties of Sr 2 VO 4−δ was investigated. Single phase polycrystalline materials of Sr 2 VO 4−δ with δ =0.18, 0.29, 0.38 were synthesized with the solid state reaction. It was revealed by the Rietveld analyses of X-ray diffraction data that the tetragonal distortion of VO 6 octahedron increased with increasing δ. Electrical resistivity measurements showed that all the samples were semiconductive. In magnetic measurements, a spin glass-like behavior imposed by a large diamagnetism was observed at temperatures below about 33K. The diamagnetism became larger for larger δ. The spin glass-like behavior is considered due to the occurrence of the random magnetic field caused by the oxygen deficiency.

Crystal Structures and Physical Properties of Layered Perovskite Compounds Srn+1VnO3n+1-δ (n=1,2,3 and ∞)

Single-phase polycrystalline materials of a series of layered perovskite compounds Sr2VO3. 64 (n=1, δ =0.36), Sr3V2O7. 01 (n=2, δ =0), Sr4V3O9. 60 (n=3, δ =0.4), and SrVO2. 84 (n=∞, δ =0.16) were synthesized by the solid-state reaction in flowing hydrogen atmosphere. The crystal structures were determined by X-ray diffraction with Rietveld analysis and the electrical and magnetic properties were investigated. The n=1, 2, and 3 compounds have tetragonal structures (14/mmm) and the a-axis lattice constant increases with increasing n. The n=1 compound is a semiconductor and the n=2, 3, and ∞ compounds exhibit metallic behaviors. The resistivity at room temperature decreases as n increases. The magnetic susceptibility for the n=2 and 3 compounds involves both Curie-Weiss and temperature-independent terms, while the n=∞ compound exhibits a temperature-independent susceptibility.