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  • (1997) Han, Shaowei; Zhao, Yong; Gu, Genda; Russell, Graeme; Koshizuka, N
    Journal Article

  • (1997) Russell, Graeme; Gu, Genda; Zhao, Yong; Han, Shaowei; Koshizuka, N; He, Ying
    Journal Article
    We report experimental studies of transport properties of superconducting Bi2Sr2CaCu2O8+δ (Bi-2212) bicrystals with various degrees of high quality [001] twist grain boundaries. We find similar resistive onset temperature and field for both the grain-boundary and the constituent single crystals. Critical current across the grain boundaries is essentially independent of twist angle. These results show that the strength of superconducting coupling along the c-axis of [001] twist grain boundaries does no depend on misorientation angle.

  • (1997) Han, Shaowei; Zhao, Yong; Gu, Genda; Russell, Graeme; Koshizuka, N
    Journal Article
    Superconducting fluctuations have been studied by systematic measurements of the in-plane paraconductivity in Bi2Sr2CaCu2O8 single crystals with different resistivity anisotropies. It has been observed that the interlayer coupling strength decreases dramatically with the anisotropy of the sample, which significantly influences the dimensional behaviour of the in-plane paraconductivity. For all the samples studied, the in-plane paraconductivity is in good agreement with the Lawrence and Doniach model. For the sample of highest resistivity anisotropy, the behaviour of the in-plane paraconductivity is basically two-dimensional, but deviates significantly from two-dimensional behaviour as the resistivity anisotropy decreases.

  • (1997) Han, Shaowei; Zhao, Yong; Zhang, Hua; Gu, Genda; Russell, Graeme; Koshizuka, N
    Journal Article
    A resistivity anomaly near the superconducting transition temperature is observed in the ab-plane of as-grown Bi2Sr2CaCu2O8 (Bi-2 2 1 2) single crystals. The resistivity at the peak is much larger than the normal state resistivity around 100 K. The peak vanished gradually with increasing the applied magnetic field. I---V curves of the Bi-2 2 1 2 samples also exhibit a peak close to the transition steps, vanishing gradually with increasing intrinsic granularity of high-Tc superconductors.

  • (1997) Han, Shaowei; Zhao, Yong; Gu, Genda; Russell, Graeme; Koshizuka, N
    Journal Article
    Superconducting fluctuations have been studied by systematic measurements of the in-plane paraconductivity in Bi2Sr2CaCu2O8 single crystals with different resistivity anisotropies. It has been observed that the interlayer coupling strength decreases dramatically with the anisotropy of the sample, which significantly influences the dimensional behaviour of the in-plane paraconductivity. For all the samples studied, the in-plane paraconductivity is in good agreement with the Lawrence and Doniach model. For the sample of highest resistivity anisotropy, the behaviour of the in-plane paraconductivity is basically two-dimensional, but deviates significantly from two-dimensional behaviour as the resistivity anisotropy decreases.

  • (1997) Han, Shaowei; Zhao, Yong; Gu, Genda; Russell, Graeme; He, Ying; Koshizuka, N
    Journal Article
    Differential resistivity, I-V characteristics, and voltage noise have been measured to study the vortex dynamics in Bi2Sr2CaCu2O8+x single crystals. The sample shows a crossover from three to two dimensional behaviour as the magnetic field is higher than a crossover field of 365 Oe. Below the crossover field, the sample show a vortex lattice melting in pinned vortex state as well as in the flux flow state. During the melting, a remarkable voltage noise was observed. The I-V curve measurements reveal that the irreversibility line does not overlap with the melting ling in H-T plane. The separation between these two lines is greatly enhanced when the applied field is over the crossover field.

  • (1997) Zhang, Hua; Qin, X; Zhao, Yong; He, Ying; Feng, Q
    Journal Article
    Samples of Bi1.7Pb0.3Sr2Ca2Cu3O10+y (2223) annealed in different atmospheres and having different value of Tc and oxygen contents were obtained and examined by a wide range of measurements as well as theoretical calculation. A roughly quantitative relationship among Tc, oxygen content, c direction thermal expansion coefficient, and mismatch factors are established. It is revealed that the mismatch is important for superconductivity.

  • (1997) Xu, M; Zhang, Kai; Jaeger, H; Hinks, D; Crabtree, G; Goregtta, K; Zhao, Yong; Choi, C
    Journal Article
    The magnetization of melt-textured Y-123 and single crystal La-214 has been measured in magnetic field up to 5.5 T using a SQUID magnetometer. Partial and nearly complete flux jumps were observed at about 10 K in Y-123 and 5 K in La-214 single crystals, respectively.

  • (1997) Han, Shaowei; Zhao, Yong; Gu, Genda; Russell, Graeme; Koshizuka, N
    Journal Article
    High-quality Bi-2212 single crystals with a transition temperature of 91 K were annealed in vacuum at 550 oC for 10, 20, 40 and 72 h. AC susceptibility measurements showed that Tc and Tc increased with increasing annealing time ta in the case of short-time annealing (ta40 h). However, as the annealing time was further increased to 72 h, the samples became non-superconducting. The results of X-ray diffraction showed that the lattice parameter of the crystal in c-axis increased with the annealing time, indicating the decrease of the oxygen content. Raman spectra revealed that the intensities of the peaks at 290 and 650 cm - 1 corresponding to the OBi vibration modes were gradually enhanced with the increase of annealing time as well as with the decrease of oxygen content, which supported the model that the excess oxygen atoms were located in the bismuth layer interstitially.

  • (1997) Zhao, Yong; Zhang, Hua; Du, X; He, Ying; Feng, Q
    Journal Article
    Superconducting transition temperature (Tc), hole concentration (nc), and crystal structure for Bi1.7Pb0.3Sr2Ca2Cu3Oy (2223) polycrystals and Bi2Sr2CaCu2Oy (2212) single crystals annealed in different atmospheres have been measured. It is found that the consequence of annealing in O2 is mainly the modification of the oxygen in Cu---O planes, which is different from that in N2 where the change is in the Bi-O planes. The result provides a good explanation for the complicated changes of the Tc with the annealing conditions.