The high-pressure high-temperature phase diagram of calcium fluoride from classical atomistic simulations

TL;DR

This study maps the phase diagram of calcium fluoride under pressure and temperature using classical molecular dynamics, revealing multiple phase boundaries, triple points, and the influence of atomic interactions on melting lines.

Contribution

It provides a detailed phase diagram of CaF2 with new predictions of triple points and analyzes atomic interactions affecting melting behavior.

Findings

Identification of three triple points involving different phases.

Prediction of phase boundaries within accessible pressure-temperature ranges.

Role of short-range repulsive and long-range attractive interactions in melting lines.

Abstract

We study the phase diagram of calcium fluoride (CaF2) under pressure using classical molecular dynamic simulations performed with a simple pairwise interatomic potential of the Born-Mayer-Huggings form. Our results obtained under conditions 0 < P < 20 GPa and 0 < T < 4000 K reveal a rich variety of multi-phase boundaries involving different crystal, superionic and liquid phases, for all which we provide an accurate parametrization. Interestingly, we predict the existence of three special triple points (i.e. solid-solid-superionic, solid-superionic-superionic and superionic-superionic-liquid coexisting states) within a narrow and experimentally accessible thermodynamic range of 6 < P < 8 GPa and 1500 < T < 2750 K. Also, we examine the role of short-ranged repulsive (SR) and long-ranged attractive (LA) atomic interactions in the prediction of melting lines with the finding that SR Ca-F and LA F-F contributions are most decisive.