Quantitative temperature determination from in-situ EXAFS measurements in shock-compressed Pt

Knowledge of temperature in shock compressed metals is a longstanding experimental need. To determine temperature in laser-shocked Pt, single-pulse (∼100-ps duration) extended x-ray absorption fine structure (EXAFS) measurements were obtained for shock stresses from 72 to 325 GPa. In contrast to x-ray diffraction (XRD) measurements, EXAFS provides local structural information and, thus, is not affected by shock-induced microstructural changes. Pt x-ray absorption spectra were recorded while a planar shock wave was propagating through the Pt sample. Fits to the shocked-state EXAFS data provided Pt lattice parameters and mean-squared relative displacements (MSRDs) for nearest-neighbor Pt atoms. Pt temperatures in the shocked state were determined from the MSRDs using the correlated Debye and correlated Einstein models. These Pt temperatures were consistent with both the Hugoniot temperatures (calculated by integration along the Hugoniot) and from published first-principles calculations for shock pressures up to 200 GPa. Above 200 GPa, deviations were observed between the temperatures from EXAFS and the calculated Hugoniot temperatures, likely due to anharmonic effects. The present results demonstrate that single-pulse synchrotron EXAFS measurements in laser-shocked solids can be used to quantitatively determine temperature at extreme pressure-temperature conditions.