[en] Li-intercalated layered perovskites Li_xAB₂Na_n-3Nb_nO_3n+1 (A=K, Rb, Cs; B=Ca, Sr, Ba) with n=3 and 4 have been prepared by an electrochemical technique. For the Li_xAB₂Nb₃O₁₀ superconducting materials, the value of T_c has been found to increase up to about 5-6 K as the a-axis length increases. For Li_xCsBa₂Nb₃O₁₀ with the largest a-axis length, however, superconductivity does not appear. In addition, Li_xKCa₂NaNb₄O₁₃ shows no superconductivity

[en] The X-ray microbeam diffraction from each particle leads to a deeper structural characterization, i.e. inter-particle structural fluctuation, of powdery compound. Here, we performed X-ray microbeam diffractions of Na_xCo_1−zNi_z[Fe(CN)₆]_y at BL40XU beamline of SPring-8. In the whole region of z, the inter-particle structural fluctuation is negligible in the as-grown powder. We found that the average (d-bar₀-bar₁-bar₂-bar) of the spacing (d₀₁₂) of the (012) plane decreases with X-ray irradiation time (t). The standard deviation (σ) of d₀₁₂ steeply increases with t from 0.006 Å at t = 1 s to 0.031 Å at t = 60 s, indicating that inter-particle structural fluctuation is induced by the X-ray irradiation. (author)

[en] The deep insight of a layered perovskite ruthenate Sr₂RuO₄ with unconventional superconducting ground state has embarked on further research of other ruthenates A_n+1Ru_nO_3n+1 where diverse ground states with different A and n have been revealed by purified crystals. In this review article, our recent achievements will be described with mainly focusing on the electronic structure and related physical properties of bilayered system (Sr₃Ru₂O₇, Ca₃Ru₂O₇) and rhodate Sr₂RhO₄, on the basis of the underlying physics of correlated multiband system Sr₂RuO₄. (author)

[en] Sr₃Mo₂O₇ is a member of the Ruddlesden-Popper type series of Sr_n+1Mo_nO_3n+1 with n=2, a so-called double layered perovskite. We have successfully synthesized polycrystalline samples of single-phase Sr₃Mo₂O₇ with the aid of Ti₂O₃ as p(O₂) buffer. The phase-pure samples allowed us to perform measurements of the electrical resistivity and the magnetic susceptibility on Sr₃Mo₂O₇ for the first time. The resistivity revealed that Sr₃Mo₂O₇ is a metallic conductor from 300 K to 30 mK. The Pauli-paramagnetic behavior is observed in the susceptibility. This means that Sr_n+1Mo_nO_3n+1 for n=1, 2, and ∞ all show the Pauli-paramagnetic metal behavior, in contrast to Sr_n+1Ru_nO_3n+1 of an electronic analogue series. (author)

[en] Single crystals of layered perovskite Sr₂RhO_4-δ (δ=0.0 and 0.1) are successfully grown by the floating-zone method. Stoichiometric single crystals (Sr₂RhO_4.0) are obtained by O₂-annealing the as-grown crystals (Sr₂RhO_3.9). Sr₂RhO_4.0 and Sr₂RhO_3.9 show quasi-two-dimensional Fermi-liquid behavior at low temperatures, whereas there are large differences in the anisotropy of electrical resistivity ρ_c(3 K)/ρ_ab(3 K) and Wilson ratio R_w between Sr₂RhO_4.0 and Sr₂RhO_3.9: ρ_c(3 K)/ρ_ab(3 K)=2400 (19000) and R_w=3.8 (6.4) for Sr₂RhO_4.0 (Sr₂RhO_3.9). The differences observed between the temperature dependence of the in-plane electrical resistivity (T<15 K), magnetic susceptibility (T<300 K) and specific heat (T<10 K) of Sr₂RhO_4.0 and Sr₂RhO_3.9 are mainly derived from those between the density of states and band structure near the corresponding Fermi level. This indicates that the changes in these physical properties, which are accompanied by oxygen defects in the Sr₂RhO_4-δ system, can be explained by the rigid band model. Moreover, these results suggest that t_2g band-filling can be controlled by adjusting the oxygen defect content δ in the Sr₂RhO_4-δ system. Although many similarities are observed in this study between the physical properties of Sr₂RhO_4.0 and Sr₂RuO₄. Sr₂RhO_4.0 does not exhibit superconductivity down to 36 mK. (author)

[en] We have successfully synthesized a double-layered perovskite compound Sr₃Mo₂O₇ by an improved process. The adjustment of O₂ partial pressure of less than 10^-21 atm was indispensable for the synthesis, and we realized it by using the oxygen buffer agent Ti₂O₃. Sr₃Mo₂O₇ was successfully indexed in a body-centered tetragonal space group I4/mmm in our XRD pattern analysis. We measured the electrical resistivity from 30 mK to 300 K and the magnetic susceptibility from 0.48 to 300 K. Sr₃Mo₂O₇ had a metallic conduction and an almost temperature-independent susceptibility. The difference between the Mo oxides and the V counterparts, which are very similar structurally, is discussed

[en] We report on the crystallographic structure of the layered perovskite iridate Sr₃Ir₂O₇, investigated using transmission electron microscopy. The space group was found to be Bbcb (D2h22, No. 68 in the International Tables for Crystallography) at 315K. A very fine twin structure with 90^o rotation with respect to the c-axis was observed. The crystal structure at temperatures lower than 285K, where a phase transition from paramagnetism to weak ferromagnetism is known to occur, was also examined. There was no difference in the extinction rule for the diffraction patterns between the two phases. We conclude that there is no change in the space group for this magnetic transition. There still remains the possibility of a change in the rotation angle of IrO₆ octahedrons and a corresponding change in the interatomic distance between Ir and O, though