Local structure of solid and liquid Au as a function of temperature by x-ray absorption spectroscopy

Abstract

Accurate Au $L$-edge EXAFS (extended x-ray absorption fine structure) spectra of elemental Au have been collected and analyzed in a wide range of temperatures from 80 to 1400 K in the solid and liquid phases. Suitable samples for high-temperature measurements in the liquid phase were obtained by in situ reduction of an organic precursor. The data analysis was carried out using reliable multiple-scattering calculations including relativistic corrections (GnXAS), especially important for this heavy element. Simultaneous ${L}_{1}$-, ${L}_{2}$-, and ${L}_{3}$-edge refinements were performed and local structural results were compared with those obtained in previous studies based mainly on x-ray diffraction experiments. In the solid phase, an increased asymmetry of the first-neighbor distribution is observed for increasing temperatures while the average distance is found to be compatible with present thermal expansion data. The structure refinement of liquid Au was carried out considering the short-range contribution to the pair distribution function $g(r)$, using available x-ray diffraction data as a constraint for long-range order. We have shown that EXAFS is extremely sensitive to the local structure and that the $g(r)$ of liquid Au is characterized by a clear shift of the foot of the $g(r)$ and a slight shortening of the position of the maximum as compared with the previous data. The present data put to a test advanced computer simulations based on embedded atom models.