Four chemically distinct iron voitaites of composition A2R52+Q33+ Al(SO4)12∙18H2O where (A, R, Q) are respectively (K, Fe, Fe) (true voltaite), (K, Fe, In), (NH4, Mn, Fe), and (Tl, Cd, Fe) were prepared by Mereiter who had previously done an X-ray structure determination on this material. These samples were studied by the Mössbauer effect to determine the site preference of Fe2+ and Fe3+ between two nonequivalent octahedrally coordinated sites M(1) and M(2): Magnetization measurements show that the magnetic ions have their free spin moment and that ferrimagnetic ordering takes place below 1 K in the cases where (A, R, Q) in the formula are (K, Fe, Fe), (NH4, Mn, Fe), and possibly in the case (Tl, Cd, Fe). The material (K, Fe, In) is antiferromagnetic with θ = −3 K.
SrFe2(PO4)2: Ab initio Structure Determination with X-Ray Powder Diffraction Data and Unusual Magnetic Properties.