The basal plane oxygen dependence of YBa₂Cu₃O_7-x anelastic relaxation and orthorhombic to tetragonal phase transition

Abstract
Measurements of the elastic energy dissipation coefficient and of the dynamic Young's modulus were performed on polycrystalline YBa₂Cu₃O_7-x by the vibrating reed technique and torsional pendulum, in the frequency range 1-5000 Hz. The stoichiometry of the samples was varied in the range x = 0.02 - 0.7. From the isothermal modulus measurements a strong softening stage characterizing the onset of the ortho-tetragonal transformation was observed. The long time isotherms give an activation energy of 0.9 = 0.1 eV. Two relaxational damping peaks have been observed and attributed to the short range oxygen dynamics in the well oxygenated and oxygen deficient superconducting phases. On the basis of these results models for the structural transformation linked to oxygen out diffusion and for the oxygen dynamics in different stoichiometric conditions are discussed.