NaMgF₃: A low‐pressure analog of MgSiO₃

Abstract

Using first principles computations we show that NaMgF 3 perovskite undergoes the same series of phase transitions as MgSiO 3 perovskite, that is, the post‐perovskite transition and the dissociation into CsCl‐type NaF and cotunnite‐type MgF 2 . These fluorides also undergo the same series of phase transitions as MgO and SiO 2 , the dissociation products of MgSiO 3 . Since the phase transformations in NaMgF 3 are not accompanied by any soft mode, we compute quasi‐harmonic free energies and the respective phase boundaries. They have positive and negative Clapeyron slopes, respectively, like MgSiO 3 . However, the transition pressures in NaMgF 3 are much lower and could be easily achieved in diamond anvil experiments. Therefore NaMgF 3 should be a good low‐pressure analog of MgSiO 3 .