4:45 PM - 5:00 PM
[SIT23-12] Crystal chemistry and compressibility of Fe0.5Mg0.5Al0.5Si0.5O3 and FeMg0.5Si0.5O3 silicate perovskites at pressures up to 95 GPa.
Keywords:silicate perovskite, single crystal X-ray diffraction , Mössbauer spectroscopy
We investigate crystalline materials with two compositions, FeMg0.5Si0.5O3 and Fe0.5Mg0.5Al0.5Si0.5O3, recovered after experiments in Kawai-type multi-anvil apparatus. After full sample characterization in terms of chemical composition, crystal structure, and iron oxidation state, we performed a series of compressibility experiments in diamond anvil cells up to 95 GPa. During compression, we collected single crystal X-ray diffraction patterns as well as Mössbauer spectra, which allowed us to follow up changes in crystal chemistry and Fe spin state during compression.
Our compressibility study on the Al-rich sample together with previously published data allowed us to reconstruct FeAlO3 end-member compressibility. We found that FeMg0.5Si0.5O3 has a previously unknown structure: the low-pressure phase is corundum-related type (space group R3), and above about 15 GPa it transforms to a new silicate double-perovskite. An outstanding feature of the silicate double perovskite structure is two individual octahedral sites; one occupied by Si only, and the other by iron and magnesium. Combining single crystal X-ray diffraction data and results of Mössbauer spectroscopy, we were able to decipher the crystal chemistry behaviour of this phase during iron spin crossover, which is detectable by both compressibility changes of individual polyhedra and variation of Mössbauer hyperfine parameters.