Single-Crystal Elasticity of MgO at High Pressure and Temperature

Abstract:

Periclase (MgO) is a material of key importance to Earth sciences: it is one of the most abundant minerals in Earth’s lower mantle. It has the simple NaCl structure with no phase transition at least up to 200 GPa and also has very high melting temperatures above 3000 K. These wide stability ranges of MgO cover high-pressure and high-temperature conditions corresponding to the Earth's lower mantle. Therefore, precise knowledge of the thermal elastic properties of MgO, major end-members of constituent mineral phases of the lower mantle, under high pressure and high temperature condition is crucial for constructing the accurate mineralogical model of the Earth's lower mantle. Here we have measured the single-crystal elasticity of MgO using in situ Brillouin spectroscopy and X-ray diffraction at simultaneous high pressure-temperature conditions up to 33 GPa and 900 K in an externally-heated diamond anvil cell. Using the third-order Eulerian finite-strain equations to model the elasticity data, we have derived the aggregate adiabatic bulk, K_S0, and shear moduli, G₀, at ambient conditions: K_S0=162.9 (6) GPa (the value in parentheses represents propagated uncertainties) and G₀=130.7 (8) GPa, respectively, consistent with literature results. The pressure derivatives of the bulk and shear moduli at 300K are (∂K_S/∂P)_T=4.06 (22) and (∂G/∂P)_T=2.75(±0.18), respectively, which are also consistent with previous literature results. We also derived the temperature derivatives of these moduli at constant pressure. Our results here provide accurate insights into seismic profiles and mineralogical models of the lower mantle region.