Field-Induced Phase Transitions in Relaxor Ferroelectrics

摘要

The Landau free energy expansion as a function of three-dimensional polarization for perovskite relaxor ferroelectrics is examined to find effects of large electric fields in causing transitions from one ferroelectric state to another. Our examination of field-induced effects includes a fourth order expansion to obtain the Landau parameters for the observed temperature- and field-induced rhombohedral (R) → tetragonal (T) transitions in an (001)-cut 0.70Pb(Mg_(1/3)Mn_(2/3))O_3-0.30PbTiO_3 (PMN-30%PT) crystal. These parameters enabled us to predict the appearance of an orthorhombic (O) phase in (110)-cut PMN-30%PT crystals under an applied field. These results show that also for field-induced effects, the Landau expansion shows qualitative agreement with experiment for relaxor ferroelectrics.