Alternating current field effect on the freezing temperature of relaxor ferroelectrics

Alternating current-field effects on the freezing temperature of La-modified lead magnesium niobate-lead titanate crystalline solutions for compositions near to the morphotropic phase boundary have been studied by dielectric spectroscopy. Charge imbalance due to La substitution (0-10 at.%) in [Pb(Mg1/3Nb2/3)O-3](0.65)(PbTiO3)(0.35) was compensated by changing the B-site cation ratio. The frequency dispersion in the dielectric constant was found to increase with increasing La substitution. Relaxor-like dielectric characteristics were induced for La concentrations greater than 5 at.%. It was also found that the dielectric constant maximum (epsilon'(max)) increased and the temperature of epsilon'(max) decreased with increasing ac field. In addition, a threshold electric field was observed above which nonlinearities became evident in the dielectric response and the freezing temperature was reduced. (C) 1999 American Institute of Physics. [S0021-8979(99)05701-1].