Cation-size control of structural phase transitions in tin perovskites

The structural evolution at 300 K of the series Sr x Ba 1− x SnO 3 and Sr x Ca 1− x SnO 3 at x = 0.2 intervals has been determined by powder neutron diffraction. All Sr x Ca 1− x SnO 3 samples ( x = 0–1) have the Pbnm superstructure. In the series Sr x Ba 1− x SnO 3 , the x = 1.0 and 0.8 samples have the Pbnm superstructure. The x = 0.6 sample has a second orthorhombic structure with space group Imma . There is a tetragonal I 4/ mcm phase at x = 0.4 and the undistorted cubic structure for x = 0.2 and BaSnO 3 . The octahedral tilt angles show a smooth variation with average A cation radius over the range of superstructures described by mean field theory close to the transition. The transitions are also analysed via the variation of spontaneous strains.