ANELASTIC RELAXATION AND INTERNAL STRAIN IN LEAD MAGNESIUM NIOBATE RELAXORS

Non-linear internal friction measurements have been carried out on lead magnesium niobate with 10 at.% lead titanate. The purpose of these measurements was to investigate the field dependence of the elastic and anelastic responses, and to determine how the response depends on the amplitude of an applied stress. The linear elastic response was found to stiffen at all bias levels with the maximum electroelastic coupling occurring near the Vogel-Fulcher freezing temperature. A strong frequency dependence of the kinetics of the anelastic relaxation was found at low measurements frequencies. These data are compared with recent high-frequency results. The existence of an inhomogeneous internal strain has been found from the line broadening of the (220) and (321) diffraction peaks. On application of an electrical field the internal strain is relieved by the development of a macrostrain which is shown to be the electrostrictive strain. It is proposed that the local electrostrictive strains are dynamic in nature and are at the origin of the anelastic relaxation. Strong elastic non-linearities, both an elastic softening and hardening under stress, have also been observed. These results are interpreted as a stress activation of the internal deformation process.