High-Pressure Study of Perovskites and Postperovskites in the (Mg,Fe)GeO System.

The effect of incorporation of Fe on the perovskite (Pbnm) and postperovskite (Cmcm) structures was investigated in the (Mg,Fe)GeO system at high pressures and temperatures using laser-heated diamond anvil cell and synchrotron X-ray diffraction. Samples with compositions of Mg# ≥ 48 were shown to transform to the perovskite (∼30 GPa and ∼1500 K) and postperovskite (>55 GPa, ∼1600-1800 K) structures. Compositions with Mg# ≥ 78 formed single-phase perovskite and postperovskite, whereas those with Mg# < 78 showed evidence for partial decomposition. The incorporation of Fe into the perovskite structure causes a decrease in octahedral distortion as well as a modest decrease in bulk modulus (K) and a modest increase in zero-pressure volume (V). It also leads to a decrease in the perovskite-to-postperovskite phase transition pressure by ∼9.5 GPa over compositions from Mg#78 to Mg#100.