MOSSBAUER STUDIES OF FE2+ IN IRON LANGBEINITES AND OTHER CRYSTALS WITH LANGBEINITE STRUCTURE

Fe-57 Mossbauer spectra have been measured at various temperatures bet ween 4.2 K and 300 K for iron langbeinites A(2)Fe(2)(SO4)(3) with A = K, NH4, Rb, Tl and magnesium, manganese and cadmium langbeinites doped with Fe2+. The spectra revealed several contributions whose isomer sh ifts and quadrupole splittings have been obtained by fitting program r outines. For the high-temperature cubic phases two crystallographicall y non-equivalent iron sites have been identified, characteristic of Fe 2+ in the high-spin state. Abrupt changes of the quadrupole couplings indicated phase transitions; in some cases, the spectra have also reve aled several sites for Fe2+ in low temperature phases. From the temper ature dependences, phase transition temperatures, crystal field splitt ings and Debye temperatures have been derived.