Yu Daoqi

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.

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.

Raman spectrum of Ba-Y-Cu-O system

Abstract The Raman spectra of a set of samples with nominal composition Ba x Y 1−x CuO 3 (0.005 ⩽ x ⩽ 0.8) which are synthesized under the same condition have been measured. It is observed that the main characters of Raman spectrum are quite different for the two groups of samples with Ba concentration being 0.3 ⩽ x ⩽ 0.8 and 0.005 ⩽ x ⩽ 0.075 respectively. It just coincides with the results two types of phase structures and the difference in superconductivity related to the two ranges of composition. Based on a comprehensive analysis of the results above, the authors suggest that the Raman peak near 605cm -1 likely corresponds to the vibration of CuO 6 octahedra breathing-mode, which play an important role in this system for achieving high transition temperature.

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.

Superconducting oxide Dy-Ba-Cu-O with TC(π=0) beyond 90K

Abstract The superconducting oxide DyxBa(1−x)CuO3 has been successfully prepared by the ceramic technology. The superconducting critical temperature, TC, of the sample of composition x=0.625 is 94K, the transition width δTc=1.5K and Tc (π=0)=90.2K. The a.c. magnetic susceptibility measurements show a large diamagnetism at 94K and a saturation of diamagnetic susceptibility near 80K. Although the element Dy has magnetic moment the superconducting transition temperature Tc is as high as that in Y-Ba-Cu-O system. This might mean that Cu-O or Cu-O-Ba system has an essential role for the high-Tc superconductivity.