Vibrational response and temperature of shock-compressed Pt: <i>In situ</i> extended x-ray absorption fine structure measurements to 325 GPa
Stefan J. Turneaure, Pinaki Das
Abstract
Single-pulse ($\ensuremath{\sim}100$-ps duration) extended x-ray absorption fine structure (EXAFS) measurements were obtained in laser-shocked Pt to examine atomic vibrational properties and to determine temperatures for shock pressures from 72 to 325 GPa. Pt x-ray absorption spectra were recorded while a planar shock wave was propagating through the Pt sample. The absorption spectrum corresponding to the shocked Pt was obtained by subtracting the ambient Pt contribution from the measured absorption spectrum. Fits to the shocked-state EXAFS data provided Pt lattice parameters consistent with the known Pt Hugoniot and the mean-squared relative displacements (MSRDs) for nearest-neighbor Pt atoms. Pt temperatures in the shocked state, estimated from the MSRDs using the correlated Debye model and correlated Einstein models, were consistent with both the Hugoniot temperatures calculated by integration along the Hugoniot and with the Hugoniot temperatures from published first-principles calculations. However, the agreement between the Hugoniot temperatures from EXAFS measurements and the calculated Hugoniot temperatures is not as good above 200 GPa, likely due to anharmonic effects. The present results demonstrate that single-pulse synchrotron EXAFS measurements in laser-shocked solids are useful for quantitative temperature determination and for examination of vibrational properties, including anharmonicity, at extreme pressure-temperature conditions.