Acoustic measurements on high- tc superconductors in the systems YBaCuO and Bi,PbSrCaCuO

Abstract

Longitudinal and transverse sound velocity and attenuation measurements as a function of temperature (4.2–280 K) and frequency (3–30 MHz) have been carried out in compounds of the type YBaCuO and Bi,PbSrCaCuO. The elastic properties of the ceramic samples, characterized by bulk modulus and Poisson ratios, are strongly affected by the microstructure (grain size, density) and the oxygen stoichiometry; YBa 2Cu 3O 7 − δ samples of different δ values have different Poisson ratios ( ν ortho < ν tetra ). Anelastic processes in the absorption were found in orthorhombic and tetragonal YBaCuO samples. A single thermally activated Debye process was observed with an activation energy H = 90 meV and an attempt frequency ν 0≈ 10 11 Hz. This was derived from the line width of the absorption peaks and the shift of the absorption maximum with frequency.