Ruan Yaozhong

The superconducting properties in Bi2−xSbxSr2Ca2Cu3Oy compounds (x=0.05, 0.1, 0.15, 0.2)

Abstract Superconducting properties of a new series Bi 2−x Sb x Sr 2 Ca 2 Cu 3 O y ( x =0.05, 0.1, 0.15, 0.2) have been reported in this paper. All of these samples have two superconducting transitions. The first superconducting transition is at about 120 K, zero resistance temperature is about 75 K. A new high- T c phase appears because of the substitution of Sb in the Bi-Sr-Ca-Cu-O system

Structural Characteristics of 2212-Phase Single Crystal in the Bi-Sr-Ca-Cu-O Superconductor

A single crystal of Bi-Sr-Ca-Cu-O 2212 superconducting phase has been studied by combining the Laue method with the method of X-ray diffractometry. It is suggested that the single-crystal structure of a superconductor is a modulated structure of a three-dimensional period coexisting with a two-dimensional lattice. In the structure, the Bi-concentrated bands, which form a three-dimensional modulated structure that corresponds to the results observed in high-resolution electron microscopy, do not entirely enter the parent structure lattice, but divide the parent structure into oxygen-deficient pervoskitelike layers. The pervoskitelike layer has a quasi-two-dimensional structure. The element modulation of Sr and Ca appears in the two-dimensional lattice, which is caused by the effect of Bi-concentrated bands. Meanwhile, the superlattice is formed on the ab plane. The three-dimensional structure of periodic modulation is formed by the pervoskitelike layer and Bi-concentrated band as a unit.

Superconducting properties in Bi2−x−yPbxSbySr2Ca2Co3Oz (x=0, 0.1, 0.3, 0.5; y=0, 0.1)

Abstract The temperature of zero resistance of the previously reported 120K superconductor in the BiSbSrCaCuO system was 75 K. We added Pb to the BiSbSrCaCuO system, so that the temperature of zero resistance was raised to 108 K.

Anistropic thermoelectric power of a superconducting Bi2Sr2CaCu2O8 crystal in the a-b plane

Abstract The resistivity and thermoelectric power of Bi 2 Sr 2 CaCu 2 O 8 single crystals were measured in the a - b plane. The ratio ϱ a /ϱ b is 1.5–1.8. The thermoelectric power in the a - b plane was found to be anisotropic for the first time. The thermoelectric power data can be fitted by the formula S = AT + B + C / T . We suggest that the anisotropic properties may be caused by the anisotropic structural features of the crystal.

Zero resistance at 117 K in Bi1.6Pb0.4Sr2Ca2Cu2+xOy compounds

In the Pb-doped Bi-Sr-Ca-Cu-O system, optimization of the composition and heat treatment conditions at which a greater amount of the high-Tcphase forms has been reported in our early paper [1], where the temperature of zero resistance was 107K. Recently, we have achieved zero resistance at 117 K and observed an a.c. susceptibility step at around 150 K by changing the Cu composition in the Bi1.6Pb0.4Sr2Ca2Cu2+xOy system (x=0, 0.4, 0.8, 1.2, and 1.6).

Transport properties in single phase superconductor Ba2YCu3O9-δ

Abstract The electrical resistivity and the thermopower are measured on the single phase superconductor Ba2YCu3O9-δ (δ=2.1). The results indicate that the temperature dependences of the resistance and thermopower exhibit typical metallic behaviour, and the sample conducts via electrons at high temperatures. The behaviour of the thermopower can be described with Motts semi-classical model. The specific heat of electrons in normal state has been estimated 780mJ/K·mole at 200K, i.e. γ=3.9mJ/K2·mole. Unusual phonon-drag effect is observed above the superconducting transition temperature Tc. Below Tc, the electrical resistivity and the thermopower all drop to zero corresponding to a superconducting ground state.

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.

High-Tc superconducting properties of YBa2Cu3-xSnxO7-y system

The effect of Sn concentration on the superconducting properties and structure of YBa2Cu3-xSnxO7-y system were systematically investigated. The zero resistance temperature was found to be above 90K as x ranges from 0 to 1.1. For x > 1.3, the system exhibited no superconducting properties at liquid nitrogen temperature. The results of x-ray diffraction showed a regular pattern of mixed structures of 123 phase and a new phase in the system with the increase of Sn concentration. TEM analysis suggested that the new phase might be BaSnO3 with deformed perovskite structure and about 6% of Cu were substituted by Sn in the 123 phase at x = 1.0. It is therefore likely that the new phase modulates the structure of 123 phase and stabilize the 123 phase. Although the Sn atoms enter 123 phase and occupy the Cu sites in the Cu-O chain and break the chain, the system remains with Tc > 90K. Consequently, the Cu-O chain plays a less important role in the high-Tc superconductivity.

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.