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The Energetics of Li Off-Centering in K$_{1-x}$Li$_x$TaO$_3$; First Principles Calculations

S. A. Prosandeev·E. Cockayne·B. P. Burton
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Abstract

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 supercells were 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.

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S. A. Prosandeev, E. Cockayne, B. P. Burton. 2003-05-28. The Energetics of Li Off-Centering in K$_{1-x}$Li$_x$TaO$_3$; First Principles Calculations. https://doi.org/10.1103/physrevb.68.014120

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