Short-range structure in solid and liquid CuBr probed by multiple-edge x-ray-absorption spectroscopy

Abstract

X-ray-absorption measurements of solid and liquid CuBr in the $T=295\mathrm{}–793\mathrm{K}$ range of temperature are presented. Accurate short-range structural parameters are extracted using simultaneous Cu and Br $K$-edge extended x-ray-absorption fine-structure (EXAFS) refinement in the framework of the multiple-scattering GNXAS method for data analysis. In solid CuBr we find an increasing asymmetry of the first-neighbor $g_{\mathrm{CuBr}}\mathrm{}\left(r\right)\mathrm{}$ distribution function as a function of temperature. The foot and the most probable value of the first-neighbor distribution are found to shift up to about 0.09 Å toward shorter distances from 295 to 670 K, while the long-range part of distribution broadens at high temperatures. Results are discussed taking into account previous neutron diffraction and EXAFS results. A complete account of our EXAFS experiment on liquid CuBr is also reported. The short-range Cu-Br distribution is extracted showing evidence for nearly covalent bonding and improving previous neutron diffraction results. The short-range CuBr liquid structure is found to be quite similar to that of the high-temperature solid. The excellent short-range EXAFS sensitivity and its complementarity with usual diffraction techniques for studying disordered systems are discussed.