Investigation of tetragonal distortion in the PbTiO_3–BiFeO_3 system by high-temperature x-ray diffraction

Compositions in the $(Pb_{1-x}Bi_x)$ $(Ti_{1-x}Fe_x)O_3$ solid solution system for x $\leq$ 0.7 show unusually large tetragonal distortion. High-temperature x-ray diffraction was used to study the tetragonal distortion as a function of temperature (25–700 $^oC$) for compositions (x - 0–0.7) using powders prepared by solid-state reaction in the above system. Large changes in the lattice parameters were observed over a narrow temperature range near Curie temperature $(T_C)$ for compositions near the morphotropic phase boundary (MPB)x $\simeq$ 0.7). Compositions near MPB showed a c/a ratio of 1.18 at room temperature. Polar plots of lattice constants at different temperatures indicated strong anisotropic thermal expansion with zero thermal expansion along the [201] direction.