E-T phase diagram of lead magnesium niobate relaxor ferroelectric in the Mandelstam-Brillouin scattering spectra

The results of studying the velocity of hypersonic longitudinal acoustic phonons over a wide temperature range under an applied constant electric field in the PbMg_1/3Nb_2/3O₃ (PMN) relaxor ferroelectric are reported. An analysis of the experimental data on the basis of the existing E-T phase diagrams shows the necessity of a substantial change in the current concepts. Two radically different states—with the reversible and irreversible behavior of velocity—have been observed experimentally in the induced ferroelectric phase. A modified _E-T phase diagram of the PMN crystal is suggested.