Mao Xianglei

The single phase Y1Ba2Cu3O7−δ bulk is a weak pinning superconductor

Abstract The magnetization measurement and the study of the Ic(B) characteristic have been made on a single phase sample in Y1Ba2Cu3O7−δ. The experimental results have shown that the single phase Y1Ba2Cu3O7−δ bulk is a weak pinning superconductor. The possible ways raising the critical current density were discussed.

Upper critical field measurements using pulsed magnetic fields in Bi1.6Pb0.4Sr2Ca2Cu2+xOy (x=0.8, 1.2, 1.6)

Upper critical magnetic fields of the Bi1.6Pb0.4Sr2Ca2Cu2+xOy system with x=0.8, 1.2, 1.6 were measured by a magnetoresistance method using a pulsed magnetic field. The Hc2(0) are estimated to be 45.9, 218 and 64.9 T for x=0.8, 1.2, 1.6, respectively. Hc1(T) for each composition was determined from magnetisation curves. The superconducting parameters xi , kappa and lambda were derived from experimental data. X-ray diffraction patterns show that there is no obvious change in structure. It is suggested that the coordination number of Cu strongly influences the superconductivity.

Relation between the upper critical magnetic field and La content for the Bi1.7Pb0.3Sr2-xLaxCa2Cu3Oy system

The behaviour of the electrical resistance, AC susceptibility, X-ray powder diffraction and upper critical field Hc2 were investigated for the Bi1.7Pb0.3Sr2-xLaxCa2Cu3Oy system. It was found that the transition temperature and the upper critical field are closely related to the lattice constant c of the 2:2:1:2 phase. From the X-ray diffraction analysis the authors found that the lanthanum first substitutes for calcium and then for strontium as the concentration of La is increased.

Two lower critical fields Hc1(0) in the high-Tc superconducting Bi2-xPbxSr2Ca2Cu3Oy system

Magnetization curves for the Bi2-xPbxSr2Ca2Cu3Oy system at different temperatures are reported. There are two phases with different critical temperatures. Corresponding to the two phases, two lower critical fields Hc1(0) are obtained.

Thermal expansion coefficient of single phase superconductor YBa2Cu3O7-δ

The thermal expansion coefficient of single phase superconductor YBa2Cu3O7-δ was measured by the method of differential parallelplate capacitance. An obvious decrease of volume near 205K and a small jump of the thermal expansion coefficient at Tc were observed. The pressure effect was also estimated.

Formation of thermal magnetokinks of flux lines and Its effect on magnetoresistance in high Tc superconductors

We proposed that the thermal magnetokinks in flux lines can form due to thermal activation in high Tc superconductors. This implies that a flux line is no longer a straight one. Basing on this model, we discussed preliminarily the behaviour of magnetoresistance.

Upper critical field of Bi Pb Sr Ca Cu O system

Abstract Upper critical magnetic field of Bi 1.6 Pb 0.4 Sr 2 Ca 2 Cu 2+x O y with x =0.8, 1.2, 1.6 and Bi 1.9−x Pb x Sb 0.1 Ca 2 Cu 3 O y with x=0.2, 0.3, 0.3, 0.5 were measured by magnetoresistance method under pulsed magnetic field. The H c2 was very sensitive to the Cu composition and the substitution of Pb on Bi site, but the T c and the structure change little. It is suggested that the coordination number of Cu and the BiO plane system influence the superconductivity strongly.

The magnetic properties of superconducting TlBaCaCuO system

Abstract The magnetic properties were measured on Tl Ba Ca Cu O system. It was observed that the magnetization changed with time. We suggested that is caused by flux creep and flux jump. The critical magnetic field and magnetization curve at different temperature were also measured. The experimental data showed that the Tl Ba Ca Cu O system was a type II superconductor.

The structure phase transition of the quenched YBa2Cu3O7−y with tetragonal phase

The single (123) phase of Y-Ba-Cu oxides with T-phase structure was prepared using the air-quenching technique. From the measurements of electrical resistance, thermal expansion coefficience, specific heat, ac susceptibility and XRD, it is the first time to find the existance of a structure phase transition. It is suggested to be a structure phase transition from Y-phase to O-phase. The explanation for low Tc in this system is also proposed in this paper.

The relation of localized ⨍-electrons with temperature in heavy fermion system

Abstract It is pointed out that the localized ⨍-electrons can change with temperature in Heavy Fermion System in the theory. According to different distance of ⨍-band and Fermi level, the n+-n-1 is not equal to zero in some temperature regions. The physical explanation was given.