Two-phase state of the crystal structure of (1-x)PbFe$_{2/3}$W$_{1/3}$O$_{3-x}$PbTiO$_{3}$ solid solutions ($x$ = 0.25, 0.3, and 0.35) at room temperature

The evolution of the crystal structure of (1-x)PbFe$_{2/3}$W$_{1/3}$O$_{3-x}$PbTiO$_{3}$ solid solutions depending on the PbTiO$_3$ concentration (at $x$ = 0.25, 0.3, and 0.35) near the morphotropic phase boundary has been investigated using X-ray diffraction at room temperature. It is established that all three compositions are mixtures of the cubic and tetragonal phases and that an increase in the PbTiO$_3$ concentration above 30 mol.% increases the tetragonal-phase fraction. The crystal structure parameters and contents of both phases in these solid solutions are determined. It is shown that there exist static displacements of lead ions from the main crystallographic sites at room temperature.