Mechanicalaging behavior of Pb(Zn_1/3Nb_2/3)O ₃-PbTiO₃ and Pb(Mg_1/3Nb_2/3)O ₃-PbTiO₃ single crystals

Single crystals of complex lead perovskite have attained great importance in recent times due to their exceptionally high piezoelectric and electromechanical constants. The application of these materials in practical devices will to a large extent depend on the aging and fatigue characteristics of these crystals. With this aim, the aging characteristics of 〈001〉-oriented Pb(Zn_1/3Nb_2/3)O ₃-PbTiO₃ (PZN-PT) and Pb(Mg_1/3Nb _2/3)O₃-PbTiO₃ (PMN-PT) single crystals have been studied under electrical and mechanical drive. Under continuous bipolar drive, a significant increment in the magnitude of hysteretic loss and decrement in the piezoelectric constant was observed. Subsequently, a novel experimental setup was fabricated to characterize the mechanical fatigue behavior of the piezo-single crystals. In this method, the crystals are placed between the two magnetostrictive plates and clamped. The cyclic mechanical stress is applied using strong magnetic fields. It was found that the piezoelectric constants decreased slowly at both short and long times but there is a pronounced decrement at intermediate times. This behavior is detrimental in designing reliable devices. The aging behavior of the piezocrystals improved significantly by doping. This improvement is suggested to be due to the restriction of relaxation processes and ordering of the system.