Shock Compression Response of Calcium Fluoride (CaF$_2$)

The fluorite crystal structure is a textbook lattice that is observed for many systems, such as CaF$_2$, Mg$_2$Si, and CeO$_2$. Specifically, CaF$_2$ is a useful material for studying the fluorite system because it is readily available as a single crystal. Under static compression, CaF$_2$ is known to have at least three solid phases: fluorite, cotunnite, and a Ni$_2$In phase. Along the Hugoniot CaF$_2$ undergoes a fluorite to cotunnite phase transition [1], however, at higher shock pressures it is unknown whether CaF$_2$ undergoes another solid phase transition or melts directly from the cotunnite phase. In this work, we conducted planar shock compression experiments on CaF$_2$ using Sandia's Z-machine and a two-stage light gun up to 900 GPa. In addition, we use density functional theory (DFT) based quantum molecular dynamics (QMD) simulations to provide insight into the CaF$_2$ state along the Hugoniot.\\ \\$[1]$ P. Kalita et al., \textit{Dynamic XRD, Shock, and Static Compression of CaF$_2$} This conference.\\ \\In collaboration with: Michael Desjarlais, Ray Lemke, Patricia Kalita, Scott Alexander, Sandia National Laboratories.\\ \\Sandia National Laboratories is a multi-mission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL850