SHORT-RANGE STRUCTURE IN SOLID AND LIQUID CUBR PROBED BY MULTIPLE-EDGE X-RAY-ABSORPTION SPECTROSCOPY

X-ray-absorption measurements of solid and liquid CuBr in the T = 295- 793 K range of temperature an presented. Accurate short-range structur al parameters are extracted using simultaneous Cu and Br K-edge extend ed x-ray-absorption fine-structure (EXAFS) refinement in the framework of the multiple-scattering GNXAS method for data analysis. In solid C uBr we find an increasing asymmetry of the first-neighbor g(CuBr)(T) d istribution function as a function of temperature. The foot and the mo st probable value of the first-neighbor distribution an found to shift up to about 0.09 Angstrom toward shorter distances from 295 to 670 K, while the long-range part of distribution broadens at high temperatur es. Results are discussed taking into account previous neutron diffrac tion and EXAFS results. A complete account of our EXAFS experiment on liquid CuBr is also reported. The short-range Cu-Br distribution is ex tracted showing evidence for nearly covalent bonding and improving pre vious neutron diffraction results. The short-range CuBr liquid structu re is found to be quite similar to that of the high-temperature solid. The excellent short-range EXAFS sensitivity and its complementarity w ith usual diffraction techniques for studying disordered systems are d iscussed. [S0163-1829(97)01041-2].