First‐principles calculations on MgSiO3 suggested a breakdown into MgO+ SiO2 at
pressure above 1000 GPa with an extremely large negative Clapeyron slope, isolating the
lowermost mantles of larger super‐Earths (∼ 10M⊕) from convection. Similar calculations
predicted the same type of breakdown in NaMgF3 to NaF+ MgF2 at 40 GPa, allowing for
experimental examination. We found that NaMgF3 is stable to at least 70 GPa and 2500 K.
In our measurements on MgF2 (an SiO2 analog), we found a previously unidentified phase …

X-4 GROCHOLSKI, B. ET AL.: STABILITY OF POST-PEROVSKITE IN NAMGF3 more, the
unit-cell axis ratios of the Pv and PPv phases in NaMgF3 are close to those in 42 MgSiO3,
making it an excellent analog material [Kubo et al., 2008]. 43 The breakdown product of
NaMgF3 (NaF and MgF2) are also analogs of MgO and SiO2. 44 The pressure extrapolation
between phase transitions of the analog fluorides 45 and oxides is roughly the same as the
pressure extrapolation needed to draw 46 conclusions about the breakdown reaction (a …