Thermal equation of state and thermodynamic properties of molybdenum at high pressures

A comprehensive P-V-T dataset for bcc-Mo was obtained at pressures up to 31 GPa and temperatures from 300 to 1673 K using MgO and Au pressure calibrants. The thermodynamic analysis of these data was performed using high-temperature Birch-Murnaghan (HTBM) equations of state (EOS), Mie-Gruneisen-Debye (MGD) relation combined with the room-temperature Vinet EOS, and newly proposed Kunc-Einstein (KE) approach. The analysis of room-temperature compression data with the Vinet EOS yields V-0 = 31.14 +/- 0.02 angstrom(3), K-T=260 +/- 1 GPa, and K-T'=4.21 +/- 0.05. The derived thermoelastic parameters for the HTBM include (partial derivative K-T/partial derivative T)(P) = -0.019 +/- 0.001 GPa/K and thermal expansion alpha - a(0) + a(1)T with a(0) - 1.55 (+/- 0.05) x 10(-5) K-1 and a(1) - 0.68 (+/- 0.07) x 10(-8) K-2. Fitting to the MGD relation yields gamma(0)=2.03 +/- 0.02 and q=0.24 +/- 0.02 with the Debye temperature (theta(0)) fixed at 455-470 K. Two models are proposed for the KE EOS. The model 1 (Mo-1) is the best fit to our P-V-T data, whereas the second model (Mo-2) is derived by including the shock compression and other experimental measurements. Nevertheless, both models provide similar thermoelastic parameters. Parameters used on Mo-1 include two Einstein temperatures Theta(E10) = 366 K and Theta(E20) - 208 K; Gruneisen parameter at ambient condition gamma(0) - 1.64 and infinite compression gamma(infinity)=0.358 with beta = 0.323; and additional fitting parameters m = 0.195, e(0) = 0.9 x 10(-6) K-1, and g 5.6. Fixed parameters include k - 2 in Kunc EOS, m(E1) - m(E2) - 1.5 in expression for Einstein temperature, and a(0) - 0 (an intrinsic anharmonicity parameter). These parameters are the best representation of the experimental data for Mo and can be used for variety of thermodynamic calculations for Mo and Mo-containing systems including phase diagrams, chemical reactions, and electronic structure. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4794127]