IR reflectance spectra of natural ilmenite: comparison with isostructural compounds and calculation of thermodynamic properties
Hofmeister, Anne M.
European Journal of Mineralogy Volume 5 Number 2 (1993), p. 281 - 296
published: Apr 27, 1993
ArtNo. ESP147050502006, Price: 29.00 €
Abstract Polarized single-crystal infrared (IR) reflectance spectra measured for natural ilmenite (FeTiO3) possessed the eight peaks mandated by symmetry plus weak bands attributable to overtones. IR and Raman peaks were correlated between these data and previous poly crystalline studies of 14 isostructural compounds by comparing intensity patterns. This enabled assignment of symmetries. Frequencies for unobserved bands were estimated from relationships of IR and Raman bands with cell volume and cation mass. Different trends exist for high- and low-frequency bands indicating that the former are essentially internal motions of octahedra containing X4+, while the latter are translations of the M2+. Heat capacities calculated from vibrational spectra lie 5 % below calorimetric measurements from 150 to 1100 K. Measured entropy is bracketed by the sum of lattice entropy calculated from a Kieffer-type model plus a constant magnetic contribution and the Slat plus Smag plus constant d-electron exchange and Fe-Ti charge transfer contributions. These results are consistent with electronic processes being temperature dependent, as expected for distorted octahedra. Accurate prediction of S and Cp for ferrous compounds will require knowledge of visible as well as vibrational spectra. Bulk moduli for isostructural compounds calculated from a modified Brout model lie within 5 % of experiment. KT is predicted for the eight compounds