High pressure and high temperature behaviour of alkali-halide fluorite CaF2 for technological applications

Fluorite (CaF2, space group Fm3¯m) is an alkali-earth halide mineral with important and manyfold technological applications and for these means several experimental and theoretical investigations were performed to characterize the structural, electronic, optical, and elastic properties. However, a detailed knowledge of the thermodynamics and thermoelastic properties of fluorite in a wide temperature and pressure range is still missing. In this work, density functional theory simulations using the hybrid B3LYP functional and all-electron Gaussian-type orbitals basis sets were employed to model these properties between 0 – 1000 K and from 0 GPa to 7 GPa. The calculated PVT equation of state parameters were V0T = 42.278(7) Å3, K0T = 92.14(7) GPa, K'0T = 3.56(2) using a 3rd-order Birch-Murnaghan formulation, α0 = 7.84(2) × 10–5 K−1 and α1 = 2.17(3) × 10–5 K−1/2 from a modified Holland and Powell thermal equation of state, and a variation of the bulk modulus with temperature ∂K0T/∂T = –0.0160(1) GPa K−1. The quality of the theoretical results was assessed by comparison with the few available data reported in the scientific literature, finding a general good agreement and extending the knowledge on this important technological material.