Comparative study of A-site order in the lead-free bismuth titanates M1/2Bi1/2TiO3 (M=Li, Na, K, Rb, Cs, Ag, Tl) from first-principles

Amplitudes of chemically induced distortion modes in different ordered perovskites M1/2Bi1/2TiO3 and visualisation of atomic displacements associated with distortion mode X+1 in the 001-ordered compounds Li1/2Bi1/2TiO3 and Cs1/2Bi1/2TiO3. Due to a substantial size mismatch between bismuth (green) and caesium (dark blue), incorporation of the latter leads to enhanced displacements of oxygen atoms (red) and suppresses displacements of titanium (silver) as compared to lithium (light blue) or other smaller monovalent cations.