Steven Jacobsen 1 , Jung-Fu Lin 1 , Przemyslaw Dera 1 , Guoyin Shen 2 , Vitali Prakepenka 2 ,
Ho-kwang Mao 1 and Russell Hemley 1
1
Carnegie Institution of Washington, Geophysical Laboratory
2
CARS, University of Chicago
High-pressure single-crystal diffraction studies with laboratory-source X-rays bathe the sample in a beam much larger than the crystal. Tightly focused monochromatic X-ray beams (~10
 m and smaller) now available at synchrotron sources typically result in the opposite situation, where the beam is much smaller than the sample. While having a beam smaller than the sample is advantages for many applications, it complicates the acquisition of quantitative intensity data during a moving-crystal diffraction experiment. However, micrometer-sized X-ray beams beg the opportunity to load multiple micro single-crystal samples (as many as one can handle) into the same diamond cell for comparative studies on e.g. the effects of composition on the high-pressure behavior of minerals. Diffraction patterns from each sample can be obtained separately, and under identical or similar conditions of pressure. Four single-crystals of magnesiowüstite containing 15, 24, 27, and 53 mol% FeO (as well as a crystal of Fe
0.93
O-wüstite) were loaded together into a diamond cell using a helium pressure medium. Individual diffraction patterns from each sample were taken at various pressures to 51 GPa using a MAR image plate by oscillating the cell ±10 degrees about the vertical axis on the 13-BMD beamline of GSECARS. Up to the highest pressure, the diffraction spots remain sharp and symmetric, suggesting that the integrity of single-crystal samples can indeed be maintained to at least one-half megabar in helium. At each pressure, typically 5 to 10 reflections from each sample were available for indexing, resulting in cell parameters (by full least squares) with a precision of a few parts in 10 4 . Only the wüstite sample displays the rhombohedral distortion (above ~20 GPa) over this pressure range.
Results on the equation of state of magnesiowüstite will be presented.
Multiple single-crystals of (Mg,Fe)O loaded in helium.