The volume dependence of thermal pressure in perovskite and other minerals

Abstract

This is a review paper concerning the thermal pressure, P TH, of solids and the conditions under which it is independent of volume. When P TH is independent of V, the general equation of state (EoS) reduces from P(V,T)=P 1(V,0)+P TH (V,T) to P(V,T)=P 1(V,0)+P TH V 0,T , and thus is separated into two independent mathematical functions. P 1( V,0) is the isothermal EoS. Four tests of thermoelastic data are shown to determine the T and V range in which P TH is independent of volume. Eighteen solids are examined. Most of these are minerals, but two metals, three alkali metals and three noble gases are also included. The focus is on three lower mantle minerals, MgSiO 3, MgO, and CaSiO 3. For these three minerals (∂ P TH/∂ V) T vanishes at conditions of the lower mantle, but P TH is a function of V at ambient conditions. However, for most solids, (∂ P TH/∂ V) T becomes zero at high temperature. The behavior of (∂ P TH/∂ V) T is apparently not correlated with such properties as crystal class, chemical composition, bonding type, and anharmonicity. The vanishing of (∂ P TH/∂ V) T is strictly a high temperature property of solids.