The role of polar nanoregions in relaxor ferroelectrics of lead magnesium niobate type is investigated in the framework of the spherical random bond–random-field model. Assuming that the interaction between polar nanoregions is modified by a homogeneous lattice stress, an expression for the macroscopic electrostrictive coefficients is obtained. A simple relation between the hydrostatic electrostrictive coefficient and the pressure derivative of the effective transition temperature and the Curie constant is derived.

• Received 1 July 2003

DOI:https://doi.org/10.1103/PhysRevB.69.212105