Mössbauer spectroscopy in the investigation of new mineral–related materials

Abstract

New materials based on the composition of the mineral schafarzikite, FeSb$_{2}\textit {O}_{4}$, have been synthesised. $^{57}$Fe- and $^{121}$Sb- Mössbauer spectroscopy shows that iron is present as Fe$^{2+}$ and that antimony is present as Sb$^{3+}$. The presence of Pb$^{2+}$ on the antimony sites in materials of composition FeSb$_{1.5}$Pb$_{0.5}\textit {O}_{4}$ induces partial oxidation of Fe$^{2+}_{}$to Fe$^{3+}$. The quasi-one-dimensional magnetic structure of schafarzikite is retained in FeSb$_{1.5}$Pb$_{0.5}\textit {O}_{4}$ and gives rise to weakly coupled non-magnetic Fe$^{2+}$ ions coexisting with Fe$^{3+}$ ions in a magnetically ordered state. A similar model can be applied to account for the spectra recorded from the compound Co$_{0.5}$Fe$_{0.5}$Sb$_{1.5}$Pb$_{0.5}\textit {O}_{4}$.