Generalized Weiss molecular-field basis for a phenomenological polarization model of lead magnesium niobate

A simple physical picture, useful for extended applications of a well-demonstrated phenomenological polarization model [J. C. Piquette and S. E. Forsythe, J. Acoust. Soc. Am. 101, 289 (1997)] is presented. The Weiss model of interacting dipoles (orginally suggested by Weiss for magnetic dipoles but applied here to electric dipoles) is generalized for high field levels. The generalization permits the model to describe the polarization measurements well, across a significant temperature range extending well below Tmax, for applied electric field levels as high as 1.35 MV/m. The measurements reported here were acquired from various polycrystalline samples of lead magnesium niobate (PMN) in a solid solution with lead titanate (PT) doped with lanthanum (La), having Tmax values ranging from −11 to +41 °C. Agreement between theory and data is good. (The overall rms error of fit is less than 0.5% in all cases considered.) The new model, when combined with a suitable model of hysteresis, is useful for describing a...