IR reflectance spectra of natural ilmenite; comparison with isostructural compounds and calculation of thermodynamic properties

A single crystal of ilmenite from Sannidal, Norway, was shown by EPMA to be a solid solution of Fe (sub 2) O (sub 3) 11.9 and Fe (sub 0.911) Mg (sub 0.076) Mn (sub 0.142) TiO (sub 3) 88.1 mole %. Polarized IR reflectance spectra showed the eight peaks mandated by symmetry plus weak bands attributable to overtones. Symmetries were assigned by correlation with results from 144 isostructural compounds. The high-frequency bands are essentially internal motions of octahedra containing X (super 4+) , while the low-frequency bands are translations of the M (super 2+) . Heat capacities calculated from vibrational spectra lie 5% below calorimetric measurements from 150 to 1100 K. These results and those for measured entropy are consistent with electronic processes being T dependent, as expected for distorted octahedra.