Energetics of Li atom displacements inK1−xLixTaO3:First-principles calculations

K 1 - x Li x TaO 3 (KLT) solid solutions exhibit a variety of interesting physical phenomena related to large displacements of Li-ions from ideal perovskite A-site positions. First-principles calculations for KLT supercellswere used to investigate these phenomena. Lattice dynamics calculations for KLT exhibit a Li off-centering instability. The energetics of Li-displacements for isolated Li-ions and for Li-Li pairs up to 4th neighbors were calculated. Interactions between nearest neighbor Li-ions, in a Li-Li pair, strongly favor ferroelectric alignment along the pair axis. Such Li-Li pairs can be considered "seeds" for polar nanoclusters in KLT. Electrostriction, local oxygen relaxation, coupling to the KT soft-mode, and interactions with neighboring Li ions all enhance the polarization from Li off-centering. Calculated hopping barriers for isolated Li ions and for nearest neighbor Li-Li pairs are in good agreement with Arrhenius fits to experimental dielectric data.