Molecular-dynamics prediction of structural anomalies in ferroelectric and dielectric BaTiO3-SrTiO3-CaTiO3 solid solutions.

Abstract

Molecular-dynamics calculations have been performed to explain the giant dielectric constant in the perovskite solid solution system $({\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x})\mathrm{Ti}{\mathrm{O}}_{3}$ and the absence of such anomaly for the similar solutions $({\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x})\mathrm{Ti}{\mathrm{O}}_{3}$. It is shown that this discrepancy is closely related to details of the lattice structure. Calculated pair correlation functions indicate that a local large displacement of Ti ions occurs only in $({\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x})\mathrm{Ti}{\mathrm{O}}_{3}$ for $x=0.3$, which coincides with the composition where the experimental dielectric constant reaches its maximum. By contrast, no such displacement occurs in $({\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x})\mathrm{Ti}{\mathrm{O}}_{3}$ because in this case the substitution of smaller Ca atoms for Sr induces predominately a homogeneous lattice shrinkage.