Phase diagram measurements to aid multi-phase equation of state construction

Experimental measurements of temperature and crystal structure at high pressures can be used to determine the equation of state of a material in a determined range of conditions. In shock compression experiments, the sampled states along a Hugoniot can cross multiple phase boundaries, necessitating the creation of multi-phase equation of states. Under high-power laser compression, the material’s state ranges from ambient pressure at start, to high temperatures in drive plasmas and high pressures of GPa to TPa in shocked states. In this talk, I will describe some of the experimental challenges that we have tackled in Streaked Optical Pyrometry measurements of MgO and in situ X-ray diffraction measurements of MgO, Cu, and Al₂O₃, where measurements that vary as a function of crystallographic orientation and texture grant insight into deformation pathways.

Deconvolution of optical and strength effects from plastic deformation will enable us to more accurately measure equation of states of target minerals of interest. Particularly interesting are regions of the phase diagram approaching structural transitions, especially at extreme states, where the phase stabilities and instabilities change rapidly. I will discuss how we use phase diagram measurements to help constrain equation of states and progress toward quantifying our uncertainties in their construction.