Elastic energy dissipation oxygen mobility and structural stability in YBa2Cu3O7-x

Internal friction and dynamic Youngs modulus measurements have been performed by the vibrating reed technique in the 102-104Hz and at lower frequencies 1-30 Hz by an inverted torsional pendulum, on polycristalline YBa2Cu3O7-x samples in the temperature range 300-900 K. Two relaxation damping peaks with 1.3±0.2 and 1.55±0.09 eV activation energies have been found. The relaxation strength depends on temperature and on the oxygen stoichiometry. A strong modulus softening indicative of a phase transition, is experienced for x=0.55 both in isothermal modulus measurements and during test at constant heating rate, when DTG measurements show correspondingly a maximum in the oxygen desorption rate. On the basis of the experimental results a model for the oxygen short range mobility, twinned interface mobility and oxygen out diffusion is presented and discussed. (orig.)