Mössbauer study of pentacoordinated ferric iron in orthoericssonite

抄録

Mössbauer spectra of orthoericssonite in the temperature range 78–547 K reveal very low quadrupole splittings (QS=0.26–0.31 mm/s) for pentacoordinated Fe³⁺, which is shown to be a consequence of the size of the angle between equatorial bonds and the apical bond of this site. At temperatures above 298 K the Mössbauer centroid shift (CS) decreases linearly at −8.0 (±1.1) ·10⁻⁴mm·s⁻¹ ·deg⁻¹, which is in good agreement with the theoretical value of −7.3 ·10⁻⁴mm ·s⁻¹ ·deg⁻¹. In agreement with previous chemical analyses of the studied samples minor absorption doublets caused by the presence of ferrous iron were recorded in the spectra of a sample from the Hijikuzu mine, Japan. Mössbauer spectra indicate that ferrous iron substitutes for manganese randomly at all three types of octahedral sites found in the orthoericssonite structure.