Elastic properties of polycrystalline YBa2Cu3O7−δ: Evidence for granularity induced martensitic behavior

Abstract In this work we present the study of the elastic properties of polycrystalline samples of superconducting YBa 2 Cu 3 O 7− δ prepared by the sol – gel method. The quality of all samples was checked by X-ray diffraction and scanning electronic microscopy while their physical properties were verified by transport and magnetic measurements. The elastic study was performed using the standard pulse – echo technique through measuring the phase velocity and the attenuation of ultrasonic waves (in the range of a few MHz) as a function of temperature. We have focused this study on the low temperatures interval ( T martensitic -like phase above the superconducting critical temperature T c . We argue that this peculiar behavior can be attributed to the granularity present in the samples.