Structural relationships and a phase diagram for (Ca,Sr)TiO 3 perovskites

Sets of lattice parameter data have been obtained from high resolution neutron and synchrotron x-ray powder diffraction patterns collected in situ as a function of temperature for perovskites in the (Ca,Sr)TiO 3 solid solution. An updated phase diagram is proposed in which there is a stability field for the I 4/ mcm structure at all compositions across the solid solution. The transition is close to tricritical in the composition range 0–70% SrTiO 3 component and then evolves towards second order character (Landau 246 solution) in the range 85–100% SrTiO 3 . Transition temperatures as a function of composition for and transitions at lower temperatures show a break in slope at ∼60 % SrTiO 3 . Variations of octahedral tilt angles and spontaneous strains are much the same for Pbcm structures as they are for Pnma structures. Nearly cubic lattice geometry of orthorhombic structures at intermediate compositions is ascribed to only weak coupling between octahedral tilting and the shear strain e 4 . The phase diagram topology and variations in structural evolution at different compositions indicate that there is a distinct change in the behaviour of the solid solution at ∼85% SrTiO 3 .