Phase transition in the Ruddlesden–Popper layered perovskite Li2SrTa2O7

The crystal structure of the Ruddlesden–Popper layered perovskite Li2SrTa2O7 has been characterized at various temperatures between −185 and 300 °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 (ΦΦ0) (ΦΦ0) inside the perovskite blocks. With temperature, the tilting progressively vanishes leading around 230 °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 abstractThermal evolution of Li2SrTa2O7 X-ray powder diffraction patterns showing the structural transformation from orthorhombic to tetragonal cell.Figure optionsDownload full-size imageDownload as PowerPoint slide