Abstract
Neighborite, NaMgF(3,) is used as a model system for understanding phase transitions in ABX(3) systems (e.g., MgSiO(3)) at high pressures. Here we report diamond anvil cell experiments that identify the following phases in NaMgF(3) with compression to 162 GPa: NaMgF(3) (perovskite) → NaMgF(3) (post-perovskite) → NaMgF(3) (Sb(2)S(3)-type) → NaF (B2-type) + NaMg(2)F(5) (P2 (1) /c) → NaF (B2) + MgF(2) (cotunnite-type). Our results demonstrate the existence of an Sb(2)S(3)-type post-post-perovskite ABX(3) phase. We also experimentally demonstrate the formation of the P2 (1) /c AB(2)X(5) phase which has been proposed theoretically to be a common high-pressure phase in ABX(3) systems. Our study provides an experimental observation of the full sequence of phase transitions from perovskite to post-perovskite to post-post-perovskite followed by 2-stage breakdown to binary compounds. Notably, a similar sequence of transitions is predicted to occur in MgSiO(3) at ultrahigh pressures, where it has implications for the mineralogy and dynamics in the deep interior of large, rocky extrasolar planets.