Cooperative Jahn-Teller Phase Transition inLaMnO3Studied by X-Ray Absorption Spectroscopy

Abstract

The local structure of ${\mathrm{L}\mathrm{a}\mathrm{M}\mathrm{n}\mathrm{O}}_3$ across the Jahn-Teller (JT) transition at $T_{\mathrm{J}\mathrm{T}}=750\mathrm{K}$ was studied by means of x-ray absorption near edge structure and extended x-ray absorption fine structure at the Mn $K$-edge. Our results indicate a similar electronic local structure for Mn atoms above and below $T_{\mathrm{J}\mathrm{T}}$ and a dynamical tetragonal JT distortion of $\mathrm{M}\mathrm{n}{\mathrm{O}}_{\mathrm{6}}$ octahedra above $T_{\mathrm{J}\mathrm{T}}$. The structural transition is originated by the ordering of tetragonally distorted octahedra. The entropy content of the transition is analyzed within the framework of the three-state Potts model with nearest neighbor antiferrodistortive coupling.