Order-disorder phenomena and octahedral tilting in SrTi_1-XSn_XO₃ perovskites – A structural and spectroscopic study

Abstract: Oxides of the type SrTi_1-xSn_xO₃ have been prepared using both a solid state and polymeric precursor method and characterized using high-resolution Synchrotron X-ray Diffraction and X-ray Absorption and Raman spectroscopies. The diffraction measurements demonstrate that a continuous pseudo-solid solution exists between the cubic SrTiO₃ and orthorhombic SrSnO₃ end-members with the same sequence of structures cubic ̅Pm3̅m → tetragonal I4/mcm → orthorhombic Imma → orthorhombic Pnma being observed irrespective of the preparation method. The Raman and XAS measurements revealed the presence of extensive disorder in samples treated at low temperatures, and that this disorder is reduced, but not totally eliminated, by annealing above 1300 °C. It is likely the local structure evolves similarly to that established by S-XRD for samples annealed above 1300 °C. This postulate is supported by the Ti K-edge XANES measurements that showed the local symmetry of the Ti cation evolves systematically as Sn⁴⁺ ions replace the Ti⁴⁺cations in the samples, irrespective of the temperature to which the sample had been heated.