57 Fe Mössbauer spectra from fluorinated phases of Fe 0.50 M 0.50 (M = Co,Mg)Sb 2 O 4

Fluorinated phases formed by reaction of Fe 0.5 Co 0.5 Sb 2 O 4 and Fe 0.5 Mg 0.5 Sb 2 O 4 with gaseous fluorine have been examined by 57 Fe Mössbauer spectroscopy between 298 and 5 K. The degree of oxidation of Fe 2+ to Fe 3 + has been used to quantify the amount of fluorine incorporated within the channels of the schafarzikite-related structure and enable the evaluation of the compositions as Fe 0.5 Co 0.5 Sb 2 O 4 F 0.41 and Fe 0.5 Mg 0.5 Sb 2 O 4 F 0.31. The multiplicity of components observed in the spectra recorded in the paramagnetic regime can be related to the number of near neighbour fluoride ions which lie in the channels at the same value of the crystal z - coordinate as the iron ions. Comparison of the magnetically ordered spectra recorded at lower temperatures from Co 0.5 Fe 0.5 Sb 2 O 4 F 0.41 with those recorded previously from FeSb 2 O 4 indicates that the insertion of fluoride ions into the channels of the structure does not affect the angle between the EFG and magnetic hyperfine field.