Gamma-X-ray coincidence Mössbauer emission spectroscopy on57Co/CoO

The time integral Mossbauer emission spectrum of a57Co/Co1−xO source (x ≈ 10−5) at RT consists of two single Lorentzian lines of an Fe2+ (76%) charge state and an Fe3+ (24%) aliovalent charge state. The spectrum measured by γ-X-ray coincidence spectrpscopy shows the same fraction of the aliovalent charge state, contrary to the expectation derived from the competing acceptor model as successfully applied by Tejada and Parak [1], who could explain the dependence of the formation of aliovalent charge states after the nuclear transformation on the stoichiometric parameterx. The consequences of this unexpected behaviour for the competing acceptor model are discussed.