The effect of polar nanoregions on electromechanical properties of relaxor-PbTiO3 crystals: Extracting from electric-field-induced polarization and strain behaviors
The electric-field-induced polarization and strain of Pb(Mg1/3Nb2/3)O3 (PMN) and Pb(Mg1/3Nb2/3)O3-0.27PbTiO3 (PMN-0.27PT) crystals were investigated at temperatures above their respective maximum permittivity temperatures Tm, where the macro-polarizations vanish while polar nanoregions (PNRs) still persist. The local structure of PNRs was proved to be of rhombohedral phase in PMN, while the local phase was unstable for PMN-0.27PT, leading to the isotropic spontaneous polarization of PNRs and strong anisotropic electric-field-induced strain. The electrostrictive coefficient Q33 was determined as functions of temperature and E-field, with 50% increment over temperature range of 20 ∼120 °C for PMN, being attributed to the decrease of spontaneous polarization of PNRs with increasing temperature. The results presented in this paper indicate that the local structure and spontaneous polarization of PNRs play important roles on electromechanical properties of relaxor ferroelectrics.