Temperature dependent Re L₃-edge X-ray absorption study of crystalline rhenium trioxide ReO₃

X-ray absorption spectroscopy study of crystalline ReO₃ was performed at the Re L₃-edge in the temperature interval from 77 to 670 K. The analysis of both XANES and EXAFS regions shows that in ReO₃, a progressive localization of the 5d states following the temperature increase is accompanied at T > 350 K by a distortion of the ReO₆ octahedra. The distortion increases continuously up to the ReO₃ decomposition temperature T_d ≈ 673 K and 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). The observed distortion is explained by (i) the strong electron-phonon coupling of the 5d electron with the M₃ and M′₃^Z phonons and (ii) the Jahn-Teller-like effect caused by the rhenium 5d¹ electron which becomes localized at high temperature.