Nuclear Electric Field Gradient at the Iron Sites in Ca2Fe2O5 and Ca2FeAlO5

Mössbauer spectroscopy has been used to determine the nuclear electric-field-gradient (efg) tensor parameters at the Fe3+ sites in Ca2Fe2O5 and Ca2FeAlO5. In all cases to within experimental error, the efg is axially symmetric and the z principal axis of the efg is parallel to the crystallographic b axis. Analytic expressions are developed for the relative transition probability of M1 radiation connecting I = 32 to I = 12 nuclear states for the situation in which the z principal axis of an axially symmetric efg is perpendicular to an internal magnetic field.