AUTHOR=Koemets Iuliia , Wang Biao , Koemets Egor , Ishii Takayuki , Liu Zhaodong , McCammon Catherine , Chanyshev Artem , Katsura Tomo , Hanfland Michael , Chumakov Alexander , Dubrovinsky Leonid 

TITLE=Crystal chemistry and compressibility of Fe0.5Mg0.5Al0.5Si0.5O3 and FeMg0.5Si0.5O3 silicate perovskites at pressures up to 95 GPa

JOURNAL=Frontiers in Chemistry

VOLUME=Volume 11 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2023.1258389

DOI=10.3389/fchem.2023.1258389

ISSN=2296-2646

ABSTRACT=Silicate perovskite with the mineral name bridgmanite is the most abundant mineral in the Earth's lower mantle. We investigated crystal structures and equations of state of two perovskite-type Fe 3+ -rich phases, FeMg0.5Si0.5O3 and Fe0.5Mg0.5Al0.5Si0.5O3, at high pressures employing singlecrystal X-ray diffraction and Synchrotron Mössbauer spectroscopy. We solved their crystal structures at high pressures and found that FeMg0.5Si0.5O3 phase adopts a novel monoclinic double-perovskite structure with the space group of P21/n at pressures above 12 GPa whereas Fe0.5Mg0.5Al0.5Si0.5O3 phase adopts an orthorhombic perovskite structure with the space group of Pnma at pressures above 8 GPa. Pressure induces an iron spin transition for Fe 3+ in a (Fe0.7,Mg0.3)O6 octahedral site of FeMg0.5Si0.5O3 phase at pressures higher than 40 GPa. No iron spin transition was observed for Fe0.5Mg0.5Al0.5Si0.5O3 phase as all Fe 3+ are located in a bicapped prism sites, which has a larger volume than an octahedral site of (Al0.5,Si0.5)O6.