Evolution of crystal structure of Ba and Ti co-doped BiFeO3 ceramics at the morphotropic phase boundary

Crystal structure of the Bi1-xBaxFe1-xTixO3 ceramics across the phase boundary region between the polar rhombohedral and pseudo-cubic phases has been investigated by means of X-ray and neutron diffraction, scanning electron microscopy and differential scanning calorimetry techniques. The structural measurements have revealed a decrease in the rhombohedral distortions upon increase in the dopant content followed by the stabilization of the pseudo-cubic phase at x ≥ 0.20. While temperature increase gives rise to the similar pattern of structural changes for the lightly-doped samples, an unpredictable temperature-driven strengthening of the rhombohedral distortions has been found for the compounds belonging to the phase boundary region. The study specifies the peculiarities of the temperature-driven evolution of the crystal structure depending on the structural state of the compounds at room temperature. •Evolution of the crystal structure is studied as a function of the dopant content and temperature.•An unpredictable temperature-driven strengthening of the rhombohedral distortions has been found for the compounds at MPB.•a non-vertical character of the temperature phase boundary and non-monotonous change of the phases ratio have been revealed.