The crystal chemistry of ferric iron in Fe0.05Mg0.95SiO3 perovskite as determined by Mossbauer spectroscopy in the temperature range 80-293 K

Mossbauer spectra were recorded at multiple temperatures between 80 and 293 K to study the nature of Fe(3+) in Fe(0.05)Mg(0.95)SiO(3) perovskite that had been synthesised in a multianvil press at 1650 degrees C and 25 GPa at its mimimum f(O2) stability limit. The Mossbauer data were fitted to a model with quadrupole splitting distributions (Fe(2+)) and Lorentzian lineshapes (Fe(3+) and Fe(n+)). The centre shift data were fitted to a Debye model with the following results: Theta(M) (Fe(2+))=365+/-52 K and Theta(M) (Fe(3+))=476+/-96 K. Hyperfine parameter data for Fe(3+) suggest occupation of the octahedral site only. The average valence seen by the Mossbauer effect in rapid electron exchange that occurs between Fe(2+) and Fe(3+) is calculated from the hyperfine parameters to be 2.50+/-0.07. Correction of area fractions for site-dependent recoil-free fractions gives a value for Fe(3+)/Sigma Fe of 9.4+/-1.4%, which is independent of temperature. A perovskite phase of similar composition synthesised in the multianvil press at higher oxygen fugacity gives a value for Fe(3+)/Sigma Fe of 16+/-3%, where Fe(3+) appears to occupy both sites in the perovskite structure.