Thermodynamic Properties of MgAl₂O₄ Spinel at High Temperatures and High Pressures

Abstract

Thermodynamic properties of MgAl2O4 spinel are significant in understanding the phase relations of the Earth’s crust and upper mantle, but available values from experimental measurements are limited at ambient pressure conditions to date. Based on an iterative numerical approach and experimental data from the literature, we determined the self-consistent unit-cell volume, elastic moduli, and, particularly, thermodynamic properties, including thermal expansion, heat capacity, entropy, and the Grüneisen parameter of MgAl2O4 spinel over a wide temperature and pressure range. The obtained thermal expansion, heat capacity, entropy, and Grüneisen parameter of MgAl2O4 spinel show nonlinearly and are negatively correlated with pressure. Most importantly, we found that the pressure effects on thermal expansion and entropy increase with temperature, whereas the pressure effect on the heat capacity and the Grüneisen parameter decreases to a minimum at ~400 K and ~700 K, respectively, then increases or remains almost constant above this temperature, respectively.

Keywords

• spinel
• thermal expansion
• heat capacity
• entropy
• Grüneisen parameter
• high temperatures and high pressures