Shinnosuke Minamigawa

Single High-Tc Phase Region of the Bi-Pb-Sr-Ca-Cu-O System

The phase diagram in the superconducting Bi1.68PbvSrxCavCuzOw(v=0.28, 0.32) system was investigated by means of X-ray diffraction and electrical resistivity for samples calcined in air. The results revealed that the phase was classified into four regions, a single 110 K-phase region, two types of two-phase regions (110 K phase+Ca2CuO3 and 110 K phase+80 K phase) and a three-phase region (110 K phase+Ca2CuO3+80 K phase). The single 110 K phase with a Tc of about 106–108 K exists in a fairly wide composition range, especially in the Bi1.68Pb0.32Sr1.75CayCuzOw system, 1.75y1.85 and 2.65z2.85. This means that the single 110 K phase can be easily obtained, even by the usual calcination in air in the Bi-Pb-Sr-Ca-Cu-O system.

Orthorhombic-Tetragonal Phase Boundary in YBa2Cu3O7-Δy

The orthorhombic-tetragonal phase boundary in the (Δy-T) diagram was determined by means of in situ X-ray diffraction methods for the YBa2Cu3O7-Δy. To cover the oxygen content region as widely as possible, two different methods were adopted. The first was performed under the fixed oxygen partial pressure and the second under the fixed oxygen content (deficiency Δy) of the samples. The obtained phase boundary showed a peculiar shape which differed from that proposed previously, suggesting the existence of another orthorhombic (ortho II) phase in low temperature region.

The Phase Change Due to Oxygen Content in the LnBa2Cu3Oy Compound Systems (Ln=Tm, Gd, Sm)

The phase change due to oxygen content y (7>y>6) was investigated for TmBa2Cu3Oy (TBC), GdBa2Cu3Oy (GBC) and SmBa2Cu3Oy (SBC) by means of X-ray diffraction and electrical resistivity. The phase boundary between orthorhombic and tetragonal phases moved toward the oxygen-rich side when the system changed as TBC→YBa2Cu3Oy(YBC)→GBC→SBC. The plateau in the critical temperature Tc was observed in the intermediate region of 6.7>y>6.4 for each system, supporting the existence of an orthorhombic-II phase. It seemed to exhibit a system dependence, i.e., a decrease in Tc in the order of TBC, YBC, GBC and SBC.

The Orthorhombic to Tetragonal Transition under Controlled Oxygen Content in High-Tc Superconductor YBa2Cu3Oy

The orthorhombic to tetragonal phase transition in YBa2Cu3Oy (y=6.9-Δy) compounds under fixed oxygen content and its relation to superconductivity were investigated by means of X-ray diffraction and resistivity measurement. In the quenching method, the phase transition was observed at about Δy=0.62 (800°C quenching temperature). In the region Δy=0.62–0.69, the high-temperature tetragonal phase transformed into the low-temperature orthorhombic phase by slow cooling, but at Δy>0.69 such a transformation was not observed. No essential difference in Tc was observed between different phases having the same oxygen content in the region Δy>0.5.

PREPARATION OF SUPERCONDUCTING 1201 PHASE IN THE (PB1-YCUY)SR2-XLAXCUOZ SYSTEM

An almost-single-1201-phase sample has been synthesized in the (Pb1-yCuy)Sr2-xLaxCuOz system. The sample showed the superconducting transition with the onset temperature of about 36.5 K and a zero resistivity temperature of about 31.5 K. These values were about 7 K higher than those reported by Adachi et al. The X-ray powder diffraction study showed that the almost-single phase was attained at the nominal composition of x=0.9 and y=0.5, and the crystal structure had a tetragonal symmetry with a=0.3769 nm and c=0.8697 nm.

Extended family of Sr free Bi-2201 copper oxides Bi2 + xLnyCa2 − x − yCuOz (La = La, Pr, Nd, Sm, Eu and Gd)

Abstract The extended family of Sr free Bi-2201 copper oxides has been synthesized in the Bi2 + xLnyCa2 − x − yCuOz (Ln = La, Pr, Nd, Sm, Eu and Gd) systems. The almost or nearly single-phase sample for each system was found to be obtained in a narrow composition region. Then, superconductivity was observed for the samples with Ln = La, Pr and Ndn. Among them, the sample with Ln = Nd exhibited the highest superconducting onset at about 11 K and zero resistivity at about 9 K.

Superconductivity in the Pb2Sr2-xLaxCu2Oz System

Superconductivity has been discovered in the new Pb-based copper oxide system of Pb2Sr2-xLaxCu2Oz. The maximum onset and zero resistivity temperature was about 38 K and 33 K, respectively. The ceramics had a tetragonal symmetry with a=0.5422 nm and c=1.2695 nm, which became an almost-single phase in the composition x=1.0.

Characteristics of Holes Investigated by ESR in High-Tc phase of Bi(Pb)-Sr-Ca-Cu-O System

Measurements of nonresonant and ESR absorption are made in the high-Tc phase of the Bi(Pb)-Sr-Ca-Cu-O system. Two components of ESR signals have been detected above the superconducting transition temperature Tc. One is anisotropic and the other is isotropic. The isotropic spectrum is not considered to arise from impurities. The nonresonant microwave absorption near zero magnetic field is greatly enhanced at Tc and the ESR signals are almost completely masked. The origin of the ESR is discussed in relation to doped holes.

New Pb-Based Cuprates with 1222 Structure Having No Tetravalent Ions, (Pb0.5Cu0.5)Sr2-xLn2-yLax+yCu2Oz (Ln: Gd, Dy, Ho and Er)

New Pb-based cuprates with 1222 structure have been synthesized in (Pb0.5Cu0.5)Sr2-xLn2-yLax+yCu2Oz (Ln:Gd, Dy, Ho and Er) systems having no tetravalent ions such as Ce4+ and Pr4+. The composition to obtain an almost-single phase sample for each system was found to be located within a narrow limited region. After oxygen annealing at 500°C for 100 h under partial pressure of 100 atm, all the almost-single-phase samples were semiconductors, but a sample with the nominal composition of (Pb0.5Cu0.5)Sr1.45Gd1.95La0.60Cu2Oz among them showed a diamagnetic signal starting from about 20 K.

Superconducting 2201 phase in the Bi2PrxCa2−xCuOz system

A new Sr-free Bi cuprate superconductor has been synthesized in the Bi2PrxCa2-xCuOz system. The superconducting phase was isostructural to the 2201 phase (Bi2Sr2CuOz). The almost-single phase was attained at the nominal composition of x=0.7~0.8. The sample with x=0.7 showed a superconducting onset at about 12 K and zero resistivity at about 6 K. The crystal structure had a pseudotetragonal symmetry with a=0.5381 nm and c=2.381 nm.