NaCl-CsCl structural transition in Sr2PdO3 and Sr2TiO4

Abstract

First principles investigations are conducted to explore the NaCl to CsCl phase transition of Sr2PdO3 and to predict the similar transition of the Ruddlesden-Popper type layered perovskite Sr2TiO4. Our results established that a first-order phase transition from Immm phase to Ammm phase of Sr2PdO3 occurs at around 30.6 GPa, being in good accordant with the experimental data (29 GPa). More interesting, the analogous topotactic structural phase transition from I4/mmm phase to orthorhombic Cmcm one is predicted to take place at about 66.6 GPa in Sr2TiO4, and associated with the increase of oxygen anion coordination number around strontium cation from nine to ten. Compared to the case of Sr2PdO3 with MO4 square planar motif, the influence of the occupancy of the vacant apical oxygen on the critical transition pressure has been deliberated. As far as we know, the I4/mmm→Cmcm transition in Sr2TiO4 has not been subject to detailed experimental high pressure studies yet. Furthermore, Sr2TiO4 is a prototypical Ruddlesden-Popper type perovskite, thus, this typical phase transition is probably ubiquitous in many compounds. We hope our results will motivate further studies, theoretical and/or experimental, on the high pressure behavior of the Ruddlesden-Popper series of layered perovskites.