An extended thermal pressure equation of state for sodium fluoride.

Abstract

The effect of pressure and temperature on the unit-cell volume of NaF has been measured by X-ray powder diffraction at ambient pressure between 12 and 300 K and neutron powder diffraction up to 5 GPa between 140 and 350 K. These data have been combined with high-pressure volume data at 300 and 950 K to 25 GPa and adiabatic bulk modulus data to 650 K to define an equation of state for NaF relating molar volume to both temperature and pressure. The model combines a fourth-order Birch-Murnaghan equation of state at 295 K with a Mie-Grüneisen-Debye model for thermal pressure. The parameters of the model set at 295 K and ambient pressure are as follows: reference unit-cell volume V ₀ = 14.9724 (5) cm³ mol^-1, isothermal bulk modulus K _0T  = 46.79 (14) GPa, first derivative of the bulk modulus K'_0T  = 5.72 (12), second derivative of the bulk modulus K''_0T  = -0.43 (4) GPa^-1, Debye temperature T _MGD = 459 (3) K, and Anderson Grüneisen parameters γ₀ = 1.547 (11) and q = 0.94 (18).