Phase transitions beyond post-perovskite in NaMgF₃ to 160 GPa

Area of Science:

• Mineral Physics
• High-Pressure Geophysics
• Materials Science

Background:

• Neighborite (NaMgF3) serves as a model for ABX3 systems, crucial for understanding Earth's mantle and exoplanet interiors.
• Phase transitions in ABX3 compounds at high pressures are key to interpreting geophysical data.

Purpose of the Study:

• To experimentally investigate the high-pressure phase transitions of NaMgF3 up to 162 GPa.
• To identify novel high-pressure phases and transition pathways in ABX3 systems.
• To provide experimental validation for theoretical predictions of high-pressure mineral behavior.

Main Methods:

• Diamond anvil cell experiments were used to subject NaMgF3 to extreme pressures.
• X-ray diffraction was employed to analyze the structural changes and identify resulting phases.

Main Results:

• A sequence of phase transitions was observed: perovskite → post-perovskite → Sb2S3-type (post-post-perovskite) → NaF (B2) + NaMg2F5 (P2/c) → NaF (B2) + MgF2 (cotunnite-type).
• The study experimentally confirms the existence of an Sb2S3-type post-post-perovskite phase.
• The formation of the P2/c AB2X5 phase, previously only theorized, was experimentally demonstrated.

Conclusions:

• Neighborite exhibits a complete sequence of phase transitions from perovskite to breakdown into binary compounds under compression.
• The findings validate theoretical models and highlight the potential for similar transitions in geologically significant materials like MgSiO3.
• This research has implications for understanding the mineralogy and dynamics within the deep interiors of large, rocky extrasolar planets.