Masashige Onoda

High-Tc Superconductivity in New Oxide Systems II

Superconducting transitions have been observed by resistivity measurements for several specimens of L-M-Cu-O system with L being Yb, Lu, Y, La and the mixture of Yb and La, and M being Ba and mixture of Ba and Sr. The onset transition temperature Tc becomes very close to 100 K. Since Yb-Ba-Cu-O and Lu-Ba-Cu-O have almost the same transition temperatures (Tc>90 K), the magnetic moment of Yb atoms does not seem to destroy the superconductivity in the present system. This suggests that the superconductivity occurs in certain parts of the system which are, at least, far from the Yb atom sites. Therefore M-Cu-O or Cu-O system may have an essential role in the occurrence of the superconductivity.

Superlattice structure of superconducting Bi-Sr-Cu-O system

Abstract Superlattice structure of superconducting Bi-Sr-Cu-O system with onset transition temperature of about 10K is determined by single crystal X-ray diffraction. The unit cell is described by a face-centered monoclinic lattice with space group C2 and the lattice parameters are a=26.856 A , b=5.380 A , c=26.908 A and β=113.55°. The estimated chemical formula is Bi10Sr10Cu5O29 with Z=4, which is reduced to Bi2Sr2CuO6−δ with δ=0.2 as the ideal phase. The structural unit consists of the five oxide layers, -Bi-Sr-Cu-Sr-Bi-, stacked along the a*-direction. A long-period sinusoidal modulation with very large amplitude can essentially explain the structure of this compound. The large deviations of Cu atom positions from the ac-plane caused by this modulation may be one of the origins of the rather low Tc value of the compound.

Superconductivity in TlBaCuO System

Abstract A new high-T c superconductor TlBaCuO system is found by resistivity and Meissner diamagnetism measurements. The onset transition temperature becomes as high as 20K when small amount of the Tl-substitution by other trivalent elements is carried out. The superconducting phase may be described as Tl 1+y Ba 1−y CuO x with y⪡1.

Normal state properties of La2−xSrxCuO4 and La2SrCu2Oy

Abstract Electrical resistivities, magnetic susceptibilities, Hall coefficients and thermoelectric powers of the La2−xSrxCuO4 (0.15 0.3, where the compounds are metallic but do not exhibit the superconductivity. These differences are discussed in relation to the x-dependence of the electronic state of the system. The behaviors of these quantities of La2SrCu2Oy which does not exhibit superconductivity are quite similar to those of La2−xSrxCuO4 with x>0.30. The inverse of RH has been found to be linear in temperature T, which gives us an evidence that the relation RH−1∝T is not characteristic of high-Tc oxide superconductors.

Metallic properties of perovskite oxide SrVO3

Abstract Physical properties of the M VO 3 ( M = Sr and Ca) perovskite system and the related compound Sr 8 V 8 O 25 have been studied by the electrical resistivity, magnetic susceptibility and NMR measurements. It has been pointed out that the magnetic properties of SrVO 3 are almost explained with a free electron model, where the electron-electron correlation seems to be small, and the electron transport is possibly due to the orbital mixing between the de and oxygen pπ.

Crystal Structures of (La1-xMx)2CuO4-δ(M=Sr and Ba)

Structure determinations of (La1-xSrx)2CuO4-δ and (La1-xBax)2CuO4-δ(x0.075) are carried out by single crystal X-ray diffraction. The former is tetragonal with space group I4/mmm, while the latter is orthorhombic with Pccn. Both compounds have the K2NiF4-type layered perovskite structures formed by the linkage of CuO6 octahedra. The orthorhombic distortion in the compound with Ba is found to be mainly described by the rotation of CuO6 octahedra which corresponds to the R25-mode of cubic perovskite lattice.

Anisotropy of the superconducting critical magnetic field HC2 of LaMCuO system(M = Sr and Ba)

Abstract Preliminary measurement of the superconducting critical magnetic field Hc2 of LaMCuO system (M = Sr and Ba) with layered perovskite structure has been carried out. The results show a quite large anisotropy of Hc2 indicating that the present system has a two dimensional character of the electron transport. The measured conductivities seem to be consistent with the values estimated from the observed Hc2 by use of an ideal two dimensional band with free electron mass.

Crystal structure of lithium molybdenum purple bronze Li0.9Mo6O17

Abstract The crystal structure of the molybdenum ternary oxide Li0.9Mo6O17 is determined by single-crystal X-ray diffraction. The crystal is monoclinic with space group P2 1 m and the lattice constants are a = 12.762(2) A, b = 5.523(1) A, c = 9.499(1) A, β = 90.61(1)°, Z = 2. Full-matrix least-squares refinement gives the final values of R(F) = 0.033 and Rw(F) = 0.066 for 3019 independent reflections. The unit cell contains six crystallographically independent molybdenum sites. One-third of the molybdenum atoms are located in oxygen tetrahedra, while the others are within oxygen octahedra. The structure is built up of slabs of the MoO6 octahedra. Each slab consists of three layers of distorted ReO3-type MoO6 octahedra sharing corners. The structure is rather different from that of K0.9Mo6O17, although the layered feature is still preserved. The lithium ions are located in the large vacant sites between the slabs. By the application of Zachariasens bond length-bond strength relation to the observed MoO bonds, most of the conduction electrons are found to be located in the Mo(1) and Mo(4) octahedral sites which are associated in pairs to form the Mo(1)O(11)Mo(4)O(11) double zigzag chains extending along the b-axis. Therefore the structural properties are considered to lead to the highly anisotropic electronic transport.

EPR Relaxation and Transport Phenomena in the Quasi-One-Dimensional Conductor β-NaxV2O5

The dynamical behaviors of the 3 d -electrons in β-Na x V 2 O 5 are studied by means of EPR relaxation, in the temperature range between 19 and 303 K. The anisotropy and the temperature dependence of the linewidth are found to originate mainly from the dipolar interaction between the 3 d -electrons of the excited state of the bipolaron at the V 1 site and the delocalized dilute paramagnetic state at the V 3 site. The correlation time of the fluctuating local field is estimated to be of the order of 10 -11 s. On the basis of this correlation time, the transverse conductivity is found in terms of the diffusive electron hopping motion between the V 1 and V 3 sites perpendicular to the chain axis, while the longitudinal one is interpreted as the collective motion of the bipolaron parallel to the chain axis.

Study on normal and superconducting properties of Bi4Sr3(Ca1−xYx)3Cu4Oy

Abstract Carrier concentration of high-T c oxide, Bi 2 (Sr, Ca) 3 Cu 2 O 8 has been successfully varied by the substitution of Ca atoms with Y and by a thermal treatment at relatively low temperatures in (0.9Ar + 0.1H 2 ) gas flow. Various physical properties have been measured through the metal-insulator boundary, the results of which indicate that these properties are quite similar to those of other well known high-T c oxides. The relationship between the magnetic susceptibility and the hole concentration suggests that a crossover of the character of electronic spin system takes place at the metal (superconducting)- insulator boundary from the localized and fluctuating to the band character.