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 L₃ 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 ≃ 673 K. The distortion leads to the lowering of the rhenium site symmetry from O_h(T ≤ 350 K) → D_4h(T ≃ 513 K) → C_4v(T ≃ 668 K) and is due to the electron-phonon coupling of the 5d electrons with the M₃ and M′₃^Z phonons and to the Jahn-Teller effect caused by the rhenium 5d¹ electron which becomes localized at high temperature.