Engineering

Publication Search Results

Now showing 1 - 10 of 40
  • (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

  • (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.

  • (1999) Han, Shaowei; Zhao, Yong; Choi, C; Andrikidis, C
    Journal Article
    Flux pinning force and irreversibility lines have been investigated for melt-textured YBa2Cu3Oy crystals containing Y2BaCuO5 (211) particles with an average size ranging from 20 to 0.02 microns. We found that the irreversibility lines are increasingly improved and that the pinning force as well as the Jc is greatly enhanced as the average size of the 211 particles decreases. The Fp-H curve exhibits two peaks in the samples containing very fine 211 particles (nanometer size particles), which suggests that an addition pinning mechanism is involved in this type of samples. The experimental results can be well explained with combining the interface-pinning mechanism and the match effect.

  • (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.

  • (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.