X-RAY DIFFRACTION STUDY OF MAROKITE (CAMN2O4) TO 40 GPA

Compression properties of marokite (CaMn2O4), which possesses a post-spinel structure, were determined with energy dispersive X-ray diffraction at high pressures and room temperature. All diffraction peaks are well indexed at least up to pressure of 25 GPa with an orthorhombic structure and Pbcm symmetry. Examination of unit-cell parameters as a function of pressure reveals three distinct ranges. Below 10 GPa, the material shows a non-linear compressibility, which might be attributed to Jahn-Teller effect. Compressibility is essentially linear between pressures of 10-25 GPa. Noticeable changes in compressibility of unit-cell parameters are observed above 30 GPa. Nature of these changes and a structural phase transition proposed based on the vibrational spectroscopic observation will be discussed in light of the current data.