High pressure structural study of MnGeO3 ilmenite

Abstract

Abstract The crystal structure of MnGeO3 ilmenite was refined using X-ray intensity data collected at 1 atm, 2.03 GPa, 3.25 GPa, 3.89 GPa and 4.99 GPa, all at room temperature. Compression of the unit cell is anisotropic, with c approximately twice as compressible as a, and c/a decreasing nearly linearly with increasing pressure. The isothermal bulk modulus determined from the cell volume data is 175(3) GPa if K0′ is assumed to be 4.0. The mean Mn–O distance is more than twice as compressible as the mean Ge–O distance. Within the Mn octahedral site, the longer of the two independent Mn–O bonds decreases by 1.8% in the pressure range studied whereas the shorter bond decreases by 0.8%. Similarly, the longer of the two independent Ge–O bonds is more compressible than the shorter Ge–O bond in the Ge octahedral site. Distortions of the Mn and Ge octahedra do not change significantly with pressure, and the cation sites remain fully ordered at all pressures studied.