Development of high electrically induced strain and low hysteric loss compositions for actuators

Electrically-induced strain and polarization studies of La modified (1 to 10 at%) morphotropic phase boundary Pb(Mg_1/3Nb _2/3)O₃-PbTiO₃ (PMN-PT) ceramics have been performed. Charge imbalance due to La³⁺ substitution on the A-site was compensated by: (a) B-site vacancies, and (b) changing Mg/Nb/Ti ratio on the B-site. Tendencies of non stoichiometric ordering were found to increase when La was compensated by B-site vacancies (LaPMN-PT) and to decrease for La compensation by changing Mg/Nb/Ti ratio (PLMN-PT). Quantitative analysis using Energy Dispersive X-ray Spectroscopy (EDS) revealed a continuous decrease in Nb and corresponding increase in Ti contents for La-PMN-PT with increasing La substitution. For PLMN-PT, no change in the B-site cation concentration was noticed. The spontaneous polarization and remanent strain were found to be higher for La-PMN-PT than PLMN-PT at low La contents (<8 at%) and to be lower at high La contents (>8 at%). In this study, the composition 2/65/35 was found to exhibit a maximum remanent strain of 1.6×10^-3 for LaPMN-PT and 1.4×10^-3 for PLMN-PT. The effect of non stoichiometric ordering on the dielectric properties and phase stability were then investigated for the directed purpose of developing new high-performance high-strain actuators with good micropositioning capabilities