An analysis of the high-temperature phase structure of multiferroic solid solutions of the PFW–PT

The temperature evolution of multiferroic solid solutions of the PFW–PT system, namely a (1–x)Pb(Fe_2/3W_1/3O₃)–(x)PbTiO₃ crystal structure where x = 0, 0.2, 0.3, has been studied by neutron powder diffraction in the region of the morphotropic phase boundary. The coexistence of cubic and tetragonal phases in the solutions with x = 0.2, 0.3 was found below T = 259 and 285 K, respectively. As a result of the data treatment, the atom coordinates, the occupation factors and the temperature dependences of cell parameters were determined in the cubic perovskite phase. The refinement of the crystal structure in terms of ideal perovskite exhibited anomalously large Debye–Waller factors for the lead cations, indicating the appearance of random static displacements of these cations from the ideal perovskite (0 0 0) position. Using the split-ion model we estimated the value of Pb static shifts (∼0.1 Å) from their high-symmetry positions along the [1 1 0] direction. It was shown that these shifts decrease with increasing the PbTiO₃ concentration.