Engineering

Publication Search Results

Now showing 1 - 10 of 24
  • (1995) Han, Shaowei; Gu, Genda; Zhao, Yong; Russell, Graeme; Koshizuka, N
    Journal Article
    Two types of Bi-2212 single crystals, one type having a low T c and the other having a high T¢ were annealed in air at different temperatures over the range 450°C to 750°C followed by furnace cooling. The transition temperature of the crystals with low T c (~ 56 K) increased with increase of annealing temperature, while the crystals with high Tc (~ 91 K) had just the opposite behaviour under the same annealing conditions. It is indicated that the quality of as-grown crystal has a significant effect on the superconducting properties of the annealed crystal. The c-axis values for both types of crystals decreased with increase of annealing temperature. According to the relationship between c-axis values and the oxygen content, our results confirmed the existence of a dome-shaped curve of T¢ with carrier concentration in Bi-2212 single crystal similar to that in Bi-2212 compound reported previously by Groen and de Leeuw [Physica C 159 (1989) 417]. By studying the increase of annealing time at a fixed temperature of 650°C, T¢ and ATe were found to change very little for both types of crystals. Thus, T c and AT~ were more sensitive to annealing temperature than to annealing time. XRD, SEM and EDS revealed that a small quantity of powder phase appeared after annealing at temperatures above 500°C for both types of crystals. This powder phase had the Bi-2212 composition, which indicated that the integrity of the Bi-2212 single crystals was significantly degraded by the annealing process.

  • (1998) Gu, Genda; Han, Shaowei; Lin, Zheng; Zhao, Yong; Russell, Graeme
    Journal Article

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

  • (1995) Han, Shaowei; Zhao, Yong; Gu, Genda; Russell, Graeme; Koshizuka, N
    Conference Paper

  • (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.

  • (1998) Han, Shaowei; Zhao, Yong; Gu, Genda; Russell, Graeme
    Journal Article
    During magnetoresistance measurement of Bi-2212 single crystals, we found the resistance in the c-axis direction exhibited a huge magnetic enhancement (H perpendicular to the a-b-plane) while the onset transition temperature along the c-axis showed a large depression when the magnetic fields were over a certain value (H > 180 Oe). No such phenomena were observed in small applied magnetic fields (H < 180 Oe) and in a-b-plane magnetoresistance measurements. By changing different probes (eight probes being attached to the sample, each side having four probes) for the measurement of the magnetoresistance along the c-axis with H = 2000 Oe, we found that the resistance along the c-axis in the temperature region T/Tc > 0.90 was only related to the measuring dimensions and Tc onset remained unchanged. Our results provided evidence that both Lorentz-force-independent fluctuation-induced dissipation and Lorentz-force-dependent vortex motion dissipation exist in the mixed state.

  • (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.