Abstract

The crystal structures of Ca_0.6Sr_0.4TiO₃ and Ca_0.8Sr_0.2TiO₃ perovskites have been studied at high temperatures by X-ray powder diffraction. The most likely sequence of phase transitions with increasing temperature in Ca_0.6Sr_0.4TiO₃ is the same as that shown by the system CaTiO₃–SrTiO₃ with increasing Sr content at room temperature. This sequence is: orthorhombic Pbnm, orthorhombic Bmmb, tetragonal I4/mcm and cubic Pmm. The second orthorhombic phase could not be determined in Ca_0.8Sr_0.2TiO₃, either due to the poorer resolution of the diffractometer employed or because the Bmmb phase might not have a stability field at this composition. The transition temperatures decrease on going from Ca_0.8Sr_0.2TiO₃ to Ca_0.6Sr_0.4TiO₃. Calorimetric measurements on 12 samples spanning the system CaTiO₃–SrTiO₃ then allow one to draw, in combination with the RT XRD data, the temperature vs. composition phase diagram. Phase boundaries show a linear shift toward lower Sr content with the increase of temperature, implying a negligible plateau effect near the CaTiO₃ composition, but quantum saturation occurs at low temperatures near the SrTiO₃ composition.