High-Pressure Mössbauer Studies on α-Fe2O3, FeTiO3, and FaO

Abstract

The effect of pressure has been measured on the Mössbauer resonance of α-Fe2O3, FeTiO3, and FeO. The first two compounds have very similar structures but with ferric and ferrous iron, respectively. The ferrous iron shows a significant increase in electron density at the nucleus with pressure, while the electron density at the ferric nucleus is virtually independent of pressure. The direction of the quadrupole splitting in α-Fe2O3 changes sign at about 30 kbar. This may be associated with a Morin (spin—flip) transition which occurs at 260°K at 1 atm, or with a slight relocation of the iron ion in the unit cell, or with a combination thereof. Ferrous oxide, a nonstoichiometric material crystallizing in the fcc structure, partially transforms to a magnetic phase at about 50 kbar. The apparent change in isomer shift and quadrupole splitting with pressure indicates that the splitting is due to the defect structure.