The crystal chemistry of BiFeO3-based ferroelectrics

X-ray diffraction and transmission electron microscopy have been carried out on samples in the solid solution series (BiFeO₃)_x-(PbTiO₃)_1-x at x = 1, 0.8, 0.7, and 0.6. The amplitude of the antiphase tilt rotations of the FeO₆ octahedra about the pseudocubic <111> axes in BiFeO₃ has been shown to decrease on addition of PbTiO₃. The tilt is absent in the tetragonal structure at x = 0.6. Both rhombohedral and tetragonal structures were found to coexist at x = 0.7, in the region of the morphotropic phase boundary. In addition, evidence of an intermediate phase was found in the same sample.