Alternating current field effect on the freezing temperature of relaxor ferroelectrics

Alternating current-field effects on the freezing temperature of La-modifie d lead magnesium niobate-lead titanate crystalline solutions for compositio ns near to the morphotropic phase boundary have been studied by dielectric spectroscopy. Charge imbalance due to La substitution (0-10 at.%) in [Pb(Mg 1/3Nb2/3)O-3](0.65)(PbTiO3)(0.35) was compensated by changing the B-site ca tion ratio. The frequency dispersion in the dielectric constant was found t o increase with increasing La substitution. Relaxor-like dielectric charact eristics were induced for La concentrations greater than 5 at.%. It was als o found that the dielectric constant maximum (epsilon'(max)) increased and the temperature of epsilon'(max) decreased with increasing ac field. In add ition, a threshold electric field was observed above which nonlinearities b ecame evident in the dielectric response and the freezing temperature was r educed. (C) 1999 American Institute of Physics. [S0021-8979(99)05701-1].