Shock Compression of [100] LiF to 230GPa : Solid and Liquid States*

Despite [100] lithium fluoride (LiF) being the most commonly used optical window material in dynamic compression experiments, its high stress shock response, including the onset stress of shock melting, has not been determined.   To address this need, we conducted well characterized plate impact experiments on [100]-oriented single-crystal LiF shock compressed to 231 GPa. Wave profile measurements were used to determine the Hugoniot curve and longitudinal sound speeds.  The Hugoniot data were well fit with a new linear Us-up relation providing an accurate determination of the LiF Hugoniot curve to significantly higher stresses than previous experiments.  The longitudinal sound speed measurements showed a rapid decrease between 180 and 195 GPa, showing the onset of shock induced melting.  Our results show that LiF remains transparent during the solid and liquid states examined in this work.  We also determined the Gruneisen parameter for the high-pressure liquid phase. These results provide important insight into the high pressure solid and liquid states of shock compressed LiF and demonstrate the need for an improved multiphase equation of state at high pressures and high temperatures.