Electronic Thesis and Dissertation Repository

Degree

Master of Science

Program

Geophysics

Supervisor

Dr. Sean Shieh

Abstract

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.


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