Abstract
Abstract Longitudinal and transverse sound velocity and attenuation measurements as function of temperature and frequency have been carried out in well characterised ceramic YBa2Cu3Ox samples of different oxygen content but the same controlled microstructure. At the occurrence of superconductivity we found a pronounced steplike behaviour in both bulk modulus and Poisson ratio. Together with a general decrease towards higher oxygen content an effect of 15 % is observed. Both effects are discussed in connection with the mixed valence of the Cu-3d electrons. Thermally activated relaxation processes in the sound attenuation are systematically studied in dependence of oxygen content. The derived activation energy shows a dependence on oxygen content which is attributed to oxygen vacancy ordering in the basal plane.
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