Phase transitions beyond post-perovskite in NaMgF<sub>3</sub> to 160 GPa.
basic_science · Level V
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- Record sourced from PubMed, PMID 31506347.
- Also identified by DOI 10.1073/pnas.1909446116 and PMC identifier 6765287.
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Abstract
Neighborite, NaMgF<sub>3,</sub> is used as a model system for understanding phase transitions in ABX<sub>3</sub> systems (e.g., MgSiO<sub>3</sub>) at high pressures. Here we report diamond anvil cell experiments that identify the following phases in NaMgF<sub>3</sub> with compression to 162 GPa: NaMgF<sub>3</sub> (perovskite) → NaMgF<sub>3</sub> (post-perovskite) → NaMgF<sub>3</sub> (Sb<sub>2</sub>S<sub>3</sub>-type) → NaF (B2-type) + NaMg<sub>2</sub>F<sub>5</sub> (<i>P2</i> <sub><i>1</i></sub> <i>/c</i>) → NaF (B2) + MgF<sub>2</sub> (cotunnite-type). Our results demonstrate the existence of an Sb<sub>2</sub>S<sub>3</sub>-type post-post-perovskite ABX<sub>3</sub> phase. We also experimentally demonstrate the formation of the <i>P2</i> <sub><i>1</i></sub> <i>/c</i> AB<sub>2</sub>X<sub>5</sub> phase which has been proposed theoretically to be a common high-pressure phase in ABX<sub>3</sub> 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<sub>3</sub> at ultrahigh pressures, where it has implications for the mineralogy and dynamics in the deep interior of large, rocky extrasolar planets.