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

Molecular-dynamics calculations have been performed to explain the giant dielectric constant in the perovskite solid solution system (Ba1-xSrx)TiO3 and the absence of such anomaly for the similar solutions (Sr1-xCax)TiO3. It is shown that this discrepancy is closely related to derails of the lattice structure. Calculated pair correlation functions indicate that a local large displacement of Ti ions occurs only in (Ba1-xSrx)TiO3 for x=0.3, which coincides with the composition where the experimental dielectric constant reaches its maximum. By contrast, no such displacement occurs in (Sr1-xCax)TiO3 because in this case the substitution of smaller Ca atoms for Sr induces predominately a homogeneous lattice shrinkage.