Effect of iron on the crystal structure of (Mg,Fe)SiO 3 perovskite

The perovskite form of Mg 0.981 , Fe 0.028 Cr 0.011 Si 0.979 O 3 , quenched from 26 GPa and 2173 K in a uniaxial split‐sphere‐type high‐pressure apparatus, was studied at the SUNY X3A beamline at the National Synchrotron Light Source. With a Si (111) double‐crystal monochromator and a single crystal of perovskite measuring 29×29×43 μm, intensities of 127 independent reflections were collected with sin θ/λ < 0.60 Å −1 and I 0 > 3.5σ I . This is the first‐reported single‐crystal diffraction study of a Mg‐silicate perovskite containing a significant amount of Fe or other cations. The unit cell parameters obtained through the refinement of 30 reflections are: a = 4.7823(3), b = 4.9331(3), c = 6.9026(8) Å, V = 162.84(2) Å 3 . The result of structural refinement in space group Pbnm indicates that Fe and a small amount of Cr substitute for Mg rather than for Si, contrary to the result of Jackson et al. (1987) who reported Fe in the octahedral site of a perovskite synthesized at 50 GPa and 2000 K in a diamond‐anvil cell with laser heating.