Aging and surface instability in high-Tc superconductors Conference

Larkins, GL, Jones, WK, Lu, Q et al. (1991). Aging and surface instability in high-Tc superconductors . 1477 26-33.



cited authors

  • Larkins, GL; Jones, WK; Lu, Q; Levay, C; Albaijes, D

fiu authors

abstract

  • Low-frequency surface degradation studies of the YBa2Cu3O7-x (123) and Bi-Sr-Ca-Cu-O superconducting ceramics have been performed in N2, Ar2, O2, wet and dry air. The time dependence of the surface impedance of both 123 and Bi-Sr-Ca-Cu- O bulk ceramics are measured from 100 Hz to 20 kHz at room temperatures and pressures. In humid environments the rate of degradation of 123 is dependent on the humidity and appears to be unaffected by the carrier gas. The surface impedance change due to humidity follows a power law and does not appear to saturate at a final value. In an environment without water present, the surface impedance of 123 follows an exponential curve of the form 1+e-at, where a is approximately 150 sec. This implies that the surface of the ceramic is relatively stationary and that it is losing oxygen. This oxygen loss converts the surface from a highly conductive state to an insulating state. This is supported by ESCA analysis of the exposed surface and freshly abraded or broken sample's interiors. In the ESCA spectra of the exposed surface there is a lack of Cu-O bond peaks; in the center of the same sample the Cu-O peaks are present. For the 2223 material there is an aging effect similar to the 1+e-at aging in 123 in inert and dry environments. The time constant for 2223 aging is 120-150 sec. Once again this is interpreted to imply the formation of a less conductive (nonsuperconductive) surface layer on the 2223. The precise mechanism and products of this decay are as yet unknown. In stark contrast with the results obtained on 123, there is no drastic difference between humid and dry inert environment surface impedance vs. time runs for 2223. This implies that 2223 is relatively nonreactive with respect to water.

publication date

  • January 1, 1991

start page

  • 26

end page

  • 33

volume

  • 1477