Phase transitions in Ca1-xSrxTiO3 perovskites: effects of composition and temperature

The crystal structures of Ca0.6Sr0.4TiO3 and Ca0.8Sr0.2TiO3 perovskites hav e been studied at high temperatures by X-ray powder diffraction. The most l ikely sequence of phase transitions with increasing temperature in Ca0.6Sr0 .4TiO3 is the same as that shown by the system CaTiO3-SrTiO3 with increasin g Sr content at room temperature. This sequence is: orthorhombic Pbnm, orth orhombic Bmmb, tetragonal I4/mcm and cubic Pm3m. The second orthorhombic ph ase could not be determined in Ca0.8Sr0.2TiO3, either due to the poorer res olution of the diffractometer employed or because the Bmmb phase might not have a stability field at this composition. The transition temperatures dec rease on going from Ca0.8Sr0.2TiO3 to Ca0.6Sr0.4TiO3. Calorimetric measurem ents on 12 samples spanning the system CaTiO3-SrTiO3 then allow one to draw , in combination with the RT XRD data, the temperature vs. composition phas e diagram. Phase boundaries show a linear shift toward lower Sr content wit h the increase of temperature, implying a negligible plateau effect near th e CaTiO3 composition, but quantum saturation occurs at low temperatures nea r the SrTiO3 composition.