Masahiro Shikano

Pressure dependence of the magnetic transition temperature for ferromagnetic SrRuO3

Abstract The resistance and A.C. susceptibility measurements for SrRuO3 under a hydrostatic pressure were carried out. TC decreases linearly with an increase in applied pressure at a rate ∂T C ∂P = −7.9 K·GPa −1 . TC decreases linearly with an increase in Ca content at a rate ∂T C ∂x = −2.6×10 2 K . These phenomena were discussed on the nallow band model.

Structural aspects on the variations of electric and magnetic properties of the layered compound system Srn+1VnO3n+1−δ(n=1,2,3,∞)

Abstract Variations of the electric and magnetic properties through the change in the number of perovskite slabs in the series of compounds Srn+1VnO3n+1−δ(n = 1,2,3,∞) were discussed based on the data of resistivity, magnetic susceptibility, and interatomic distances determined by the powder X-ray diffraction analysis. Change from metallic SrVO3−δ, Sr3V2O7−δ, and Sr4V3O10−δ to semiconductive Sr2VO4−δ through the change of the n could be correlated to the change in the V-O distances along the c-axis. One d electron associated with V4+ ion may occupy the 3-fold degenerate t2g d orbital in the compounds with n = 3 and ∞, the 2-fold degenerate orbitals dyz and dzx in the compound with n = 1, and non-degenerate dxy orbital in the compound with n = 2.

Synthesis and properties of a new d1 compound Sr4V3O9.8 with layered structure

Abstract A new layered compound Sr4V3O9.8 with the Sr4Ti3O10 structure was successfully synthesized and electrical resistivity and magnetic susceptibility measurements were carried out. The unit cell dimensions of Sr4V3O9.8 were found to be a = 0.38428(3) nm and c = 2.7902(2) nm. The slope of the resistivity vs temperature curve changed from slightly negative to positive at a temperature of ∼70 K as the temperature was increased. The magnetic susceptibility of the sample could be fitted by the Curie-Weiss law, χ = χ 0 + C (T - Θ) , with χ0 = 1.06 × 10−3 emu·mole−1, Θ = −66 K, and C = 5.88 × 10−2 emu·K·mole−1.

Candidate compounds for superconductivity

Non-cupreous compounds with perovskite-related structures containing V 4+ (3d 1 ), Co 3+ (3d 6 ), and Rh 3+ (4d 6 ) were synthesized and their properties were investigated. A metallic d 1 compound Sr 4 V 3 O 10-δ with the layered structure showed a semiconducting resistivity at low temperatures by an increase of the oxygen vacancies or by a substitution of V by Ti. Semiconducting perovskite-related compound LaRhO 3 with the low spin configuration of Rh 3+ (4d 6 ) could be hole-doped in the d e orbitals by the substitution of La by Sr or Ca, and showed a metallic conductivity, while LaSrRhO 4 with the K 2 NiF 4 structure and the low spin configuration could not be hole-doped by decreasing the La/Sr ratio.

Lithium insertion into ceramic SrVO3−δ

Lithium was electrochemically inserted into SrVO3−δ by using a galvanic cell: Li|1M LiClO4 in PC|SrVO3−δ. After the insertion of the amount x=0.1 in LixSrVO3−δ, metallic conductivity was maintained being accompanied by an increase of the absolute value of one order of magnitude and a very small volume increase was observed. The results indicate the possibility to use SrVO3−δ as a cathode without any conductive additives in rechargeable lithium batteries.

A Reversible Rocksalt to Amorphous Phase Transition Involving Anion Redox

The charge-discharge capacity of lithium secondary batteries is dependent on how many lithium ions can be reversibly extracted from (charge) and inserted into (discharge) the electrode active materials. In contrast, large structural changes during charging/discharging are unavoidable for electrode materials with large capacities, and thus there is great demand for developing materials with reversible structures. Herein, we demonstrate a reversible rocksalt to amorphous phase transition involving anion redox in a Li2TiS3 electrode active material with NaCl-type structure. We revealed that the lithium extraction during charging involves a change in site of the sulfur atom and the formation of S−S disulfide bonds, leading to a decrease in the crystallinity. Our results show great promise for the development of long-life lithium insertion/extraction materials, because the structural change clarified here is somewhat similar to that of optical phase-change materials used in DVD-RW discs, which exhibit excellent reversibility of the transition between crystalline and amorphous phase.