Ca. Mccammon, THE CRYSTAL-CHEMISTRY OF FERRIC IRON IN FE0.05MG0.95SIO3 PEROVSKITE AS DETERMINED BY MOSSBAUER-SPECTROSCOPY IN THE TEMPERATURE-RANGE 80-293K, Physics and chemistry of minerals, 25(4), 1998, pp. 292-300
Mossbauer spectra were recorded at multiple temperatures between 80 an
d 293 K to study the nature of Fe3+ in Fe0.05Mg0.95SiO3 perovskite tha
t 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 fitt
ed to a model with quadrupole splitting distributions (Fe2+) and Loren
tzian lineshapes (Fe3+ and Fen+). The centre shift data were fitted to
a Debye model with the following results: Theta(M) (Fe2+)=365+/-52 K
and Theta(M) (Fe3+)=476+/-96 K. Hyperfine parameter data for Fe3+ sugg
est occupation of the octahedral site only. The average valence seen b
y the Mossbauer effect in rapid electron exchange that occurs between
Fe2+ and Fe3+ is calculated from the hyperfine parameters to be 2.50+/
-0.07. Correction of area fractions for site-dependent recoil-free fra
ctions gives a value for Fe3+/Sigma Fe of 9.4+/-1.4%, which is indepen
dent of temperature. A perovskite phase of similar composition synthes
ised in the multianvil press at higher oxygen fugacity gives a value f
or Fe3+/Sigma Fe of 16+/-3%, where Fe3+ appears to occupy both sites i
n the perovskite structure.