Giant room-temperature electrostrictive coefficients in lead-free relaxor ferroelectric ceramics by compositional tuning

摘要

A thermotropic phase boundary between non-ergodic and ergodic relaxor phases is tuned in lead-free Bi_1/2Na_1/2TiO₃-based ceramics through a structural transition driven by compositional modification (usually named as “morphotropic approach”). The substitution of Bi(Ni_1/2Ti_1/2)O₃ for Bi_1/2(Na_0.78K_0.22)_1/2TiO₃ induces a transition from tetragonal to “metrically” cubic phase and thereby, the ergodic relaxor ferroelectric phase becomes predominant at room temperature. A shift of the transition temperature (denoted as T_F-R) in the non-ergodic-to-ergodic phase transition is corroborated via temperature-dependent dielectric permittivity and loss measurements. By monitoring the chemical composition dependence of polarization-electric field and strain-electric field hysteresis loops, it is possible to track the critical concentration of Bi(Ni_1/2Ti_1/2)O₃ where the (1 ? x)Bi_0.5(Na_0.78K_0.22)_0.5TiO₃-xBi(Ni_0.5Ti_0.5)O₃ ceramic undergoes the phase transition around room temperature. At the Bi(Ni_0.5Ti_0.5)O₃ content of x = 0.050, the highest room-temperature electrostrictive coefficient of 0.030 m4/C2 is achieved with no hysteretic characteristic, which can foster the realization of actual electrostrictive devices with high operational efficiency at room temperature.