Single-crystal synchrotron X-ray diffraction study of wüstite and magnesiowüstite at lower-mantle pressures

This study demonstrates the use of monochromatic synchrotron X-ray radiation of 40 keV for high-precision equation-of-state studies on sets of single crystals analysed individually in the same diamond-anvil pressure cell. Angle-dispersive zone-axis diffraction patterns were obtained from crystals of wustite-Fe_0.93O and magnesiowüstite-(Mg_0.73Fe_0.27)O to 51 GPa in a hydrostatic helium pressure medium. The rhombohedral phase of Fe_0.93O was observed above 23 GPa, and its isothermal bulk modulus (K₀) was determined to be 134 (±4) GPa, assuming K' = 4. The rhombohedral phase of Fe_0.93O is more compressible than B1-structured Fe_0.93O, with K₀ = 146 (±2) GPa. Magnesiowüstite-(Mg_0.73Fe_0.27)O remains cubic over the experimental pressure range, and has a bulk modulus of 154 (±3) GPa with K' = 4.0 (±0.1).