Dieletric anomalies in Pb_(0.7(1-x))Ca_(0.7x)La_(0.2)TiO_3

摘要

Transitions from ferroelectric to relaxorlike and then to quantum paraelectriclike behavior occur in Pb_(0.7(1-x))Ca_(0.7x)La_(0.2)TiO_3 (PCLT) with increasing x from 0.05 to 0.60. The relaxorlike behavior, which can be well fitted to the Vogel-Fulcher relation, is clearly demonstrated by the frequency dispersions of permittivity. More interestingly, a thermal hysteresis of ～5 K was observed in the temperature dependences of real and imaginary permittivity (ε′ and ε″) for PCLT with x=0.40 under both zero-field cooling and zero-field heating conditions. The compositional dependence of transition temperature T_(max) vanished with a finite slope, contrary to that of the quantum ferroelectric relation T_(max)∝(x-x_c)~(0.5).