Short-range order in solid and liquid KBr probed by EXAFS

Br K-edge EXAFS spectra of solid and liquid KBr have been performed and analysed using advanced techniques for data analysis (GNXAS). Structural results on solid KBr at room temperature and near melting are compared with molecular dynamics (MD) simulations and diffraction data. The first-neighbour distribution is found to be strongly asymmetric even at room temperature, as also shown by MD simulations. This confirms the existence of important anharmonic effects in solid KBr. MD simulations are in agreement with EXAFS data at room temperature. For solid KBr near melting, anharmonic effects become very important. In comparison with MD calculations, the rise of the first-neighbour peak is found to be steeper, while the foot of the first-neighbour distribution is found to be slightly shifted toward longer distances. Experimental short-range partial pair distribution functions g(BrK) and g(BrBr) are derived in liquid KBr for the first time. The first peak of the g(BrK) distribution is accurately determined and found to be in good agreement with MD simulations, confirming a slight contraction of the most probable Br-K distance in the liquid phase. The first peak of the g(BrBr) distribution, measured with less accuracy, is found to be sharper and slightly shifted to longer distances, lowering the overlap with the first-neighbour K shell.