Electronic Thesis and Dissertation Repository


Master of Science




Dr. Sean Shieh


Magnesiochromite (MgCr2O4) is commonly found in the Earth’s crust, upper mantle, meteorites, and possibly in lunar crust. Synchrotron X-ray diffraction measurements of MgCr2O4 using double-sided laser heating diamond anvil cell showed the dissociation of MgCr2O4 to Cr2O3+MgO at ~15 GPa and to Mg2Cr2O5+Cr2O3 below and above ~1500 K, respectively. At above 20 GPa, only a single phase CaTi2O4-type structure of MgCr2O4 was observed at 1400-2000 K. Fitting the pressure-volume data of CaTi2O4 type structure of MgCr2O4 with Birch-Murnaghan equation of state yields volume at ambient condition (V0) = 264.4(8) Å3, bulk modulus (K0) = 185.4(4) GPa, and pressure derivative of the bulk modulus (K0’) = 4; and for CaTi2O4 type structure of natural chromite: V0 = 261(1) Å3, K0 = 175.4(2) GPa, K0’ = 4, and mLd-type Mg2Cr2O5 yields: V0 = 338.9(8) Å3, K0 = 186.5(6) GPa, K0’ = 4. Obtained phase diagram and bulk modulus data provide important information to better understand the structure and dynamics of the deep earth.