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

Fluorite (CaF 2 , space group Fm 3 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 Gaussiantype 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 V 0 T = 42.278(7) & Aring; 3 , K 0 T = 92.14(7) GPa, K ' 0 T = 3.56(2) using a 3rd-order Birch-Murnaghan formulation, alpha 0 = 7.84(2) x 10 -5 K -1 and alpha 1 = 2.17(3) x 10 -5 K -1/2 from a modified Holland and Powell thermal equation of state, and a variation of the bulk modulus with temperature partial derivative K 0 T / partial derivative 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.