Extended X-ray Absorption Fine Structure Temperature Analysis at High-Energy-Density Conditions*

A critical next step in understanding high-energy-density (HED) matter is to characterize the temperature of materials at HED conditions. Temperature measurements are historically difficult at low temperature HED conditions (above 100 GPa and below 5000 K) and extended x-ray absorption fine structure (EXAFS) spectroscopy is one of the few experimental techniques capable of constraining temperature at these conditions by measuring the variation in the distances between neighboring atoms. A variety of synthetic and experimental EXAFS spectra of iron, nickel and invar (Fe₆₄Ni₃₆) were analyzed with a Bayesian inference routine to infer the atom positions using both a cumulant expansion and a parametrized ion-distribution model. The parametrized ion-distribution model was found to improve the constraint on the true ion distribution for the synthetic asymmetric systems. These ion distributions were ultimately related to the temperature of the compressed sample using a variety of models that will be discussed herein.