The low-frequency behaviour of the isotropic elastic modulus and mechanical loss tangent of modified ferro-piezo-electric ceramics were studied by using the 3-point bending technique. Measurements of these parameters, as a function of temperature, were carried out at frequencies ranging from 0.2 to 20Hz. The results revealed anomalies, in both parameters, at the transition temperature and below. The anomalies below the transition temperature exhibited wide maxima of mechanical loss, whose temperatures increased when the measuring frequency was increased. Values for activation energies were obtained which suggested the existence of mechanical relaxation mechanisms in which point defects and 90º ferro-electric domains were involved. The main species of point defect was expected to be the O vacancy.

B.Jiménez, J.M.Vicente: Journal of Physics D, 1998, 31[4], 446-52