High pressure effects on thermal properties of MgO

Abstract

Using the non-empirical Variational Induced Breathing (VIB) model, the thermal properties of periclase (MgO) under high pressures and temperatures are investigated using molecular dynamics, which includes all anharmonic effects. Equations of state for temperatures up to 3000K and pressures up to 310 GPa were calculated. Bulk modulus, thermal expansivity, Anderson-Griineisen parameter, thermal pressure, Gr/ineisen parameter and their pressure and temperature dependencies are studied in order to better understand high pressure effects on thermal properties. The results agree very well with experiments and show that the thermal expansivity decreases with pressure up to about 100GPa (•-0.73), and is almost pressure and temperature independent above this compression. It is also effected by anharmonicity at zero pressure and temperatures above 2500K. The thermal pressure changes very little with increasing pressures and temperatures, and the Griineisen parameter is temperature independent and decreases slightly with pressure.

The melting curve and premelting of MgO

“…This function, which has up to 21 parameters for O-O interactions, can be evaluated much more rapidly than doing the full quantum calculations at each time step. The resulting potential has been severely tested for thermal properties of MgO [Isaak et al, 1990;Inbar and Cohen, 1995], and we have great confidence in the potential.…”

“…Molecular dynamics simulations using the closely related VIB (Variationally Induced Breathing) model (described below) show exceptional accuracy for the equation of state of MgO, including high order properties such as the change in thermal expansivity with pressure [Inbar and Cohen, 1995]. Given the accuracy of the model for properties of the solid, it was surprising when the first experimental measurements for the melting curve of MgO showed a discrepancy of over a factor of three in the dT/dP slope, with the experiments showing a much shallower slope [Zerr and Boehler, 1994].…”

Thermodynamically self-consistent method to predict thermophysical properties of ionic oxides

“…It is clear that the proposed TSC method predicts volume vs pressure behavior Thermal expansion coefficient (a) of CaO at different (a) temperatures (zero pressure) and (b) pressures (mentioned constant temperatures). Anderson(94)[38],Oda(92) [39], Fiquet(99)[40], Smith(68)[41],Saxena(92) [42],Rao(14) [43], Karki(03)[31],Srivastava(11) [44], Srivastava(09)[45],Singh(12) [46], Inbar(95)[47] and Isaak(90)[48].…”

Ab-initio determination of high-pressure and high-temperature thermoelastic and thermodynamic properties of low-spin (Mg1-xFex)O ferropericlase with x in the range [0.06, 0.59]

“…Some thermoelastic (K T , V T , K′ T , α) and thermodynamic parameters of interest (C V , C P , S) are shown in Table 5, concerning either periclase (Isaak et al 1989;Chopelas 1990;Fei 1995;Inbar and Cohen 1995;Robie et al 1995;Dubrovinsky and Saxena 1997;Fiquet et al 1999;Karki et al 2000;Oganov and Dorogokupets 2003;Ghose et al 2006) or LS and HS ferropericlase [however, in some works the spin is not specified (Hama and Suito 1999)] with different iron contents (the thermoelastic ones are calculated numerically).…”

“…(1/K) MgO Inbar and Cohen (1995) / / / / / / 3.88E-05 Ghose et al (2006) / / / 36.58 / 26.80 / Fiquet et al (1996) / / / / / / 4.90E-05 Fiquet et al (1999) 74 . The molar quantities are converted for the primitive cell of periclase with two atoms to allow the comparison, whereas the cell volume refers to the conventional cell with eight atoms (P = 0.1 MPa, T = 298.15 K). The backslash symbol "/" means that the datum is not reported.…”