A high-temperature x-ray absorption spectroscopy study of ReO3

We present for the first time a high-temperature x-ray absorption spectroscopy study of ReO3 at the Re L(3) edge. The analysis both of the XANES and of the EXAFS regions shows that, in ReO3, a progressive localization of the 5d states following the temperature rise is accompanied at T > 350 K by a distortion of the ReO6 octahedra, which increases up to the ReO3 decomposition temperature T-d similar or equal to 673 K. The distortion leads to the lowering of the rhenium site symmetry from O-h(T less than or equal to 350 K) --> D-4h(T similar or equal to 513 K) --> C-4v(T similar or equal to 668 K) and is due to the electron-phonon coupling of the 5d electrons with the M(3) and M'(Z)(3) phonons and to the Jahn-Teller effect caused by the rhenium 5d(1) electron which becomes localized at high temperature.