Troisiéme Conférence Européenne sur les Matériaux et les Procédés Avancés
J. Phys. IV France 03 (1993) C7-2033-C7-2038
The basal plane oxygen dependence of YBa2Cu3O7-x anelastic relaxation and orthorhombic to tetragonal phase transitionE. BONETTI1, G.P. CAMMAROTA2, E.G. CAMPARI1 and A. CASAGRANDE2
1 Dipartimento di Fisica, Università di Bologna, Consorzio INFM and GNSM-CNR, via Irnerio 46, 40126 Bologna, Italy
2 Istituto di Metallurgia, Università di Bologna, CIRM, v. le Risorgimento 4, 40122 Bologna, Italy
Measurements of the elastic energy dissipation coefficient and of the dynamic Young's modulus were performed on polycrystalline YBa2Cu3O7-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.
© EDP Sciences 1993