Sun Shifang

Hall effect in single phase Ba2YCu3O7−δ

Abstract Results of resistivity, a.c. magnetic susceptibility, Hall effect and superconductivity for single phase Ba 2 YCu 3 O 7− δ are reported. The positive value of Hall constant above T c indicates that the carriers of the sample are hole-like in normal state and its concentration is about 1.1×10 21 cm -3 at room temperature. A large anomaly of R H near T c is observed which may be indicative of granular superconductivity or be related to the intrinsic quality of this class of oxides.

Superconductivity and phases of leaded Bi-Ca-Sr-Cu-O system

Abstract In this paper, two main phases are found in the Bi2-xPbxCa2Sr2Cu3Oy system One is 4334 phase, another is a new one with cell parameters a =5.09 A , b =5.18 A , and c =36.98 A . The results of ac susceptibility measurements in the Bi2-xPbxCa2Sr2Cu3Oy system there are three superconducting transition at 110K, 95–100K and 65K respectively. As the x is increased from 0.1 to 1.2, the zero resistance temperature (Tce) is raised to 107K (x=0.3-0.5) at first, then is reduced to 64K gradually.

Effects of Ag doping on the critical current density of YBa2Cu3O7−y

Abstract A series of (YBa 2 Cu 3 O 7−y ) 1−x Ag x samples were prepared using solid state reaction method. On the basis of X-ray diffraction analysis, scanning electron microscopic observation, measurements of the resistivity; a.c. magnetic susceptibility as well as the critical current density, we find that enhancing the intergranular coupling by improving the properties of grainboundaries, while the properties of grains are kept unchanged, helps to increase the critical current density. The dependences of the critical current density on the Ag content, the temperature and the magnetic field are discussed. Our results suggest that eliminating grainboundaries together with improving the properties of grains may be an effective way in raising the critical current density in bulk materials.

Electronic state and superconductivity in YBa2Cu3−xZnxOy system

Abstract The measurements of X-ray diffraction, dependence of d.c. resistance on temperature and Hall effect have been performed for YBa2Cu3−xZnxOy system. The doped samples in 1-2-3 phase all exhibit metallic behavior and the hole carrier concentration experiences a nonmonotonous variation, but still larger than that of the perfect sample. The picture of localization is applied to explain these phenomena. The TC suppression mechanism has been discussed for this system.

Localization of the electrons and superconductivity in YBa2Cu3−xNixO7−y

Abstract The crystal structure, electron transport properties in normal state and superconductivity of a series of YBa2Cu3−xNixO7−y samples (0≤×≤0.5) were investigated. With the increase of the Ni content, the resistivity in normal state increased, and the resistance-temperature coefficient changed from metallic type to semiconductive type. The intimate correlation among the superconductive critical temperature, crystal structure and resistivity, espically the correlation of Tc∼ P strongly suggested that the localization effect of the electrons be an important factor to the decrease of Tc.

The Behaviour of Negative Magnetoresistance and Hysteresis in YBa2Cu3O7-δ

By measuring the structure, superconductivity, magnetoresistance of polycrystalline single-phase YBa2Cu3O7-δ samples, the phenomena of negative magnetoresistance and the hysteresis of the magnetoresistance have been studied. An analysis of the origin of the influence of grain boundaries on the superconductivity and the electronic transport properties are given.

Superconductivity in Sr-Y-Cu-O system

Abstract A stable and reproducible superconductivity transition has been observed through a.c. magnetic susceptibility and electrical resistivity measurements in the (Srx Y1−x)CuO3−Y with x=0.375, 0.4, and 0.5. The highest Tc(π=0) is 90.5K and the width of transition δTc=1.5K.

Hall effect in superconducting oxide Ba-Y-V-Cu-O

Results of resistivity, ac magnetic susceptibility, and Hall-effect measurements for Ba1.2Y0.9V0.9Cu3O7-δ are reported. The positive value of Hall constant indicates that the material conducts via hole with a carrier concentration of 1.6×1021cm-3 at room temperature. A large anomaly in RH near Tc is observed.

Zero resistance above 90K in superconducting oxides ErBaCuO and YbBaCuO

Abstract Superconductivity transition has been observed by electrical resistance and a.c. magnetic susceptibility measurements in ErBaCuO and YbBaCuO systems. The highest T c ( ϱ =0) is 90.3K for ErBaCuO and 91K for YbBaCuO.

A new superconducting oxide GdBaCuO with Tc (ρ=0) above 92K

Abstract A new superconducting oxide GdxBa1−xCuO3−y with Tc (ρ=0) above 92K has been successfully synthesized by the ceramic technology. The samples with composition of x=0.5, 0.625 and 0.9 are all observed with high Tc superconductivity. The highest Tc for samples measured is observed in Gd0.5Ba0.5CuO3−y which has a resistive midpoint of 95K with a width of 1.5K, and a zero-resistance temperature of 92.5K. The results of a.c. magnetic susceptibility measurement are also reported.