Tomoaki Yabe

High Temperature Superconductivity at 90 K in Orthorhombic LaBa2Cu3Oy

A LaBa2Cu3Oy sample with an orthorhombic crystal structure was synthesized. It showed superconductivity with an onset temperature of 95 K and zero resistance at 80 K (midpoint 90 K). From the magnetic susceptibility measurement, about 30% of the whole volume of the sample was found to be the 90 K superconducting phase. The 90 K superconducting phase in LaBa2Cu3Oy is thus considered to have an oxygen defect perovskite structure which is most probably identical to that of the typical 90 K superconductor orthorhombic YBa2Cu3Oy.

Transport Properties of (La1-xAx)2CuO4

Various transport properties are systematically investigated for the quasi-two-dimensional superconductors, (La1-xAx)2CuO4 (A=Ba, Sr). They are compared with the calculations based on the two-dimensional tight-binding band. From this, it is inferred that the superconductivity is coexisting with Fermi surface instability, possibly a spin-density-wave which destroys a significant portion of the Fermi surface.

Study on the preparation of 90‐K superconductor LaBa2Cu3Oy

The high‐Tc superconductor LaBa2Cu3Oy has been prepared under various conditions, and characterized by x‐ray and neutron powder diffraction techniques, dc and ac magnetic susceptibility measurements, and dc resistivity measurement. It has been found that samples with excellent superconducting characteristics and also with good structural properties are obtained in a reproducible way if the following three procedures are performed: preheat treatment of La2O3 powders, sintering in N2, and low‐temperature annealing in dried O2. Long‐time annealing in undried O2 was sometimes found to degrade the grain boundaries and to lead to a lower zero‐resistance temperature.

Effect of substitution of 3d metals for Cu in Bi2(Sr0.6Ca0.4)3Cu2Oy

Abstract The effect of the substitution of 3d metals (Fe, Co, Ni and Zn) for Cu was investigated. Lattice constants, DC resistivity, Hall effect, magnetic susceptibilities in normal and superconducting phases were measured. The change of the Hall coefficient with the substitution was much smaller than those in YBa 2 Cu 3 O y or in Y or lanthanide substituted Bi 2 (Sr, Ca) 3 Cu 2 O y . The change of T c with the substitution of Fe, Co, Ni with localized magnetic moment did not differ much from that of Zn with no magnetic moment.

Orthorhombic-to-tetragonal phase transition in LaBa2Cu3Oy

It was found by high-temperature X-ray powder diffraction that LaBa2Cu3Oy undergoes an orthorhombic-to-tetragonal phase transition at around 350°C. Resistivity measurement shows that the annealing only below this transition temperature assures good superconducting characteristics in the samples.

Physical Properties of an 80 K-Superconductor: Bi-Sr-Ca-Cu-O Ceramics

The magnetization curve, tunneling spectra, and normal-state susceptibility were measured in well-characterized single-phase 80 K superconductor, Bi-Sr-Ca-Cu-O ceramic samples. The obtained result is very similar to that of other copper-oxide superconductors.

Structural study of La1+xBa2-xCu3Oy

Concerning with the existence of the solid solution La 1+x Ba 2−x Cu 3 O y the Rietveld refinement of the TOF neutron powder diffraction data s owe A at tyke orthorhombic La 1 Ba 2 Cu z O y (z⋍3) really exists as not only 90 K superconductor but also 50 K one.

ELECTRONIC PROPERTIES OF ORTHORHOMBIC LaBa2Cu3Oy

Magnetic susceptibility, Hall coefficient, and Seebeck coefficient were measured in the normal state of orthorhombic LaBa2Cu3Oy. The susceptibility is a superposition of a Curie component and the remaining component, which has a weak temperature dependence. The estimated density of states at the Fermi level is 3.8 states/eV Cu atom at room temperature. The results of Hall coefficient and Seebeck coefficient measurements suggest that the dominant carriers are holes supplied by the monovalent oxygen ions.

Superconducting properties of orthorhombic LaBa2Cu3Oy

The upper and lower critical fields of orthorhombic LaBa2Cu3Oy were measured, and superconducting parameters were derived. From these measurements, LaBa2Cu3Oy was found to be a typical type-II superconductor with extremely short coherence length of 20 A. Also, taking account of the measured normal-state parameters, both superconducting and normal-state properties in LaBa2Cu3Oy were found to be almost the same as those in LaBa2Cu3Oy.

Superconductivity, Crystal Structure and Orthorhombic-Tetragonal Phase Transition in 90 K Superconductor Orthorhombic LaBa2Cu3Oy

It was found that the onset temperature above 90 K occurs in orthorhombic LaBa2Cu3Oy but not in tetragonal one, in contrast to the previous reports. The structure of this phase was refined by the Rietveld analysis of the X-ray powder diffraction data and it was isostructural with the orthorhombic YBa2Cu3Oy. The orthorhombic-tetragonal phase transition near 350°C was found out by the high-temperature X-ray powder diffraction.