We report the results of a Mouml;ssbauer study of57Co(57Fe) in CoSO4as a function of temperature at atmospheric pressure and as a function of pressure at room temperature. In addition to the expected divalent57Fe component, one also observes a trivalent component, the relative intensity of which decreases with increasing temperature or pressure. The isomer shifts of both charge states also decrease with increasing temperature or pressure. The behavior of the large quadrupole splittings observed in each charge state is analyzed using the crystal field approximation. We also find similar results in a temperature study of CoSO4middot;7H2O at atmospheric pressure. The relative intensity of the trivalent57Fe component is considerably greater in the hydrate and also decreases with increasing temperature.
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