A distributed step-like switching model of the continuous field-driven phase transformations observed in PMN–xPT relaxor ferroelectric single crystals

The field-driven phase transformation behavior of relaxor ferroelectric single crystal PZN–xPT is discontinuous and displays well-defined forward and reverse coercive fields, whereas the same transformation in PMN–xPT is nearly continuous and occurs over a range of field levels. In analogy to the broad Curie range in relaxor ferroelectrics arising from property fluctuations at the nanometer length scale, the continuous field-driven phase transformations in PMN–xPT are modeled as a step-like series of discontinuous transformations associated with similar spatial property fluctuations. An increase in the applied field gradually increases the volume fraction of the new phase at the expense of the old phase, resulting in a continuous transition between phases. The model simulation produces excellent agreement with the measured material response of 〈0 1 1〉 cut PMN–0.32PT single crystals under conditions of cooperative stress and electric field loading.