Phase transition in the Ruddlesden-Popper layered perovskite Li{sub 2}SrTa{sub 2}O{sub 7}

The crystal structure of the Ruddlesden-Popper layered perovskite Li{sub 2}SrTa{sub 2}O{sub 7} has been characterized at various temperatures between -185 and 300 deg. C by several techniques: X-ray and neutron powder diffraction, single crystal diffraction, transmission electron microscopy and Raman spectroscopy. The low temperature structure has been confirmed to be orthorhombic Cmcm with a small octahedra antiphase tilting ({phi}{phi}0) ({phi}{phi}0) inside the perovskite blocks. With temperature, the tilting progressively vanishes leading around 230 deg. C to a tetragonal symmetry (S.G. I4/mmm). This reversible phase transition, followed by X-ray and neutron thermodiffraction and thermal Raman measurements, is considered as of second order. An attribution of the Raman bands based on normal mode analysis is proposed. - Graphical abstract: Thermal evolution of Li{sub 2}SrTa{sub 2}O{sub 7} X-ray powder diffraction patterns showing the structural transformation from orthorhombic to tetragonal cell.