The nature of the orthorhombic to tetragonal phase transition in Sr1−xCaxMnO3

The orthorhombic–tetragonal phase transition in the perovskite series Sr1−xCaxMnO3 0.4⩽x⩽0.6 has been studied by synchrotron X-ray powder diffraction. At room temperature the Ca rich oxides x⩾0.45 have the orthorhombic Pbnm superstructure whereas Sr0.6Ca0.4MnO3 is two phases with both tetragonal I4/mcm and orthorhombic Pbnm. Analysis of the octahedral tilts suggest the co-existence of these two phases is a consequence of a first-order I4/mcm to Pbnm transition. The evolution of the structure of Sr0.5Ca0.5MnO3 with temperature is also described and this is found to evolve from orthorhombic to tetragonal and ultimately cubic.