A. Ichinose

Pressure effect on Tc of (Yb0.7Ca0.3)(Ba0.8Sr0.2)2Cu3Oz with various oxygen contents

Abstract Pressure dependence of T c for (Yb 0.7 Ca 0.3 )(Ba 0.8 Sr 0.2 ) 2 Cu 3 O z with different oxygen contents is investigated up to 2GPa. The pressure derivative dT c /dP shows decreasing positive values for the decreasing positive values for the region with (dT c / dp pl >0, and negative values for that witth (dT c /d p pl c /dP depend on the hole concentration in the CuO 2 plane. These results indicate that the application of pressure plays a role of hole redistribution between the CuO chain and CuO 2 plane sites.

Possibility of Superconductivity Destruction Caused by Neither the Reduction of Hole Concentration nor Impurity Doping

Raman scattering spectra of single crystals of (Eu2/3Ce1/3)2 Ba2/3Eul/3)2Cu3O8+z (Eu-223) and (Er2/3 Ce1/3)2(Ba2/3La1/3)2 Cu3O8+z (ErLa-223) have been measured at room temperature. A peak due to magnon-pair scattering has been observed at 2600 cm−1 in the spectra of semiconducting Eu-223 but not in superconducting Eu-223. The exchange integral is estimated as 960cm−1, which is nearly the same as that of semiconducting YBa2Cu3O6+z. On the other hand, magnon scattering peak has not been seen in the spectra of nonsuperconducting ErLa-223. This fact suggests that sufficient carriers are doped in the Cu-O2 planes in this material though it does not show superconductivity.

Layered copper oxide series, (Fe, Cu) Sr2 (Y, Ce)nCu2O4+2n+z, containing multiple-MO2-unit fluorite block

Abstract We successfully synthesized new homologous compound series, (Fe, Cu)Sr 2 (Y, Ce) n Cu 2 O 4+2n+z (n=1∼7, z∼1.0). The compounds with n ≧ 2 consist of triple-perovskite block and fluorite blocks. The compound with n=1 exhibited superconductivity and those with n ≧ 2 were semiconductive. The superconducting properties of this series compounds are discussed from a crystallographic point of view.

New copper oxides, (Ba,Ca)8CaCu4O13+Z

Abstract A new copper oxide system, (Ba 1−x Ca X ) 8 CaCu 4 O 13+Z (0≦x≦0.25 and z∼0.5), was discovered. As the quenching temperature increased, the oxygen contents decreased and all the lattice constants, a, b, and c approached to the same value. On the basis of x-ray powder diffraction and electron diffraction patterns, it was considered that the stractural change from orthorhombic to tetonagonal in (Ba 1−X Ca X ) 8 CaCu 4 O 13+Z was enhanced by oxygen nonstoichiometry.

1-2-3 Superconductors with High Hole Density

(Yb1−xCax)(Ba0.8Sr0.2)2Cu3Oz (0≦ X≦ 0.4) solid solutions of the 1-2-3 (oxygen deficient triperovskite) structure have been successfully synthesized. These samples have been characterized with respect to oxygen nonstoichiometry, crystal structure and superconducting properties. The fully oxygenated samples with Z~6.8 had an orthorhombic unit cell and exhibited bulk superconductivity as shown by magnetic susceptibility measurements. Their superconducting transition temperatures decreased with increasing Ca content, X. The (Yb0.9Ca0.1) (Ba0.8Sr0.2)2Cu3Oz and (Yb0.7Ca0.3)(Ba0.8Sr0.2)2Cu3Oz samples with various oxygen content, Z (6.36≦ Z≦ 6.89 for X=0.1 and 6.1≦ Z≦ 6.78 for X=0.3) were prepared by the reduction of fully oxygenated samples. One of the samples with X=0.3 and Z=6.56 had a tetragonal unit cell and exhibited a sharp superconducting transition at 82 K. The superconducting transition temperatures (Tc) are discussed on the basis of the hole concentration in the CuO2 sheet.

Hall Effect in Oxide Superconductors Having Fluorite-Type Layers

The Hall effect at temperatures between Tc and 300 K was investigated for the superconducting ceramics of (Nd,Ce)2CuO4-y, (Ln,Sr)2CuO4-y where Ln=(Nd,Ce) or (La,Sm), and (Ln,Ce) 4 (Ln,Ba,Sr) 4Cu6Oy where Ln = Nd or (Y, La). The sign of the Hall coefficient (RH) was positive except for (Nd,Ce)2CuO4-y. The magnitude of RH for all the three compounds exhibits a broad peak around 120–150 K with respect to temperature. It is contrary to the case of the K2NiF4- and the 1:2:3-type superconductors, in which RH increases monotonically with decreasing temperature. The peak structure is not likely due to the magnetic moment of the rare earth elements, but due to the influence of the fluorite layer contained in the three compounds.