Modified Johnson model for ferroelectric lead lanthanum zirconate titanate at very high fields and below Curie temperature

A modified Johnson model is proposed to describe the nonlinear field dependence of the dielectric constant (epsilon-E loop) in ferroelectric materials below the Curie temperature. This model describes the characteristic ferroelectric butterfly shape observed in typical epsilon-E loops. The predicted nonlinear behavior agreed well with the measured values in both the low- and high-field regions for lead lanthanum zirconate titanate films. The proposed model was also validated at different temperatures below the ferroelectric-to-paraelectric Curie point. The anharmonic coefficient in the model decreased from 6.142 x 10(-19) cm(2)/V-2 to 2.039 x 10(-19) cm(2)/V-2 when the temperature increased from 25 degrees C to 250 degrees C. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3676668]