title: Demixing instability in dense molten MgSiO3 and the phase diagram of MgO.
abstract: The phase diagrams of MgSiO3 and MgO are studied from first-principles theory for pressures and temperatures up to 600 GPa and 20,000 K. Through the evaluation of finite-temperature Gibbs free energies, using density-functional theory within the generalized gradient approximation as well as with hybrid exchange-correlation functionals, we find evidence for a vast pressure-temperature regime where molten MgSiO3 decomposes into liquid SiO2 and solid MgO, with a volume change of approximately 1.2%. The demixing transition is driven by the crystallization of MgO--the reaction only occurs below the high-pressure MgO melting curve. The predicted transition pressure at 10,000 K is in close proximity to an anomaly reported in recent laser-driven shock experiments of MgSiO3. We also present new results for the high-pressure melting curve of MgO and its B1-B2 solid phase transition, with a triple point at 364 GPa and 12,000 K.
authors.affiliation: Department of Physics, Dalhousie University, Halifax, Nova Scotia, Canada B3H 3J5.
authors.forename: Brian
authors.initials: B
authors.lastname: Boates
authors.forename: Stanimir A
authors.initials: SA
authors.lastname: Bonev