A-Site Strain and Displacement in Ba1-xCaxTiO3 and Ba1-xSrxTiO3 and the Consequences for the Curie Temperature

Classical computer simulations are performed on the whole solid solution range of Ba1-xCaxTiO3 (BCT) and Ba(1-x)Sr(x)TiO3 (BST). The enthalpies and volumes of mixing are produced, and a full local structural analysis is performed. The simulations demonstrate that large degrees of disorder form in the BCT solid solution which leads to distortions in the TiO6 octahedra. Comparing the positions of Sr in BST and Ca in BCT, the position of the Sr cation is largely central within the dodecahedra while the position of the Ca is significantly off-center in many configurations. The relaxation is associated with a shift toward an eight coordinate site compared to a 12 coordinate cation. An empirical model is fitted for predicting the Curie Temperature of the solid solution based on the local structure which shows excellent agreement with experimental values.