Mossbauer spectroscopy of spinels

Soon after the discovery of the Mossbauer effect, studies were performed on spinels containing various transition metal ions (mostly Fe2+). This metho d proved very useful for investigating the local symmetry at transition met al ions. In spite of the numerous results, the correct interpretation of th e complex quadrupole split spectra is still not given for numerous spinel s tructures. Since spectra of different shapes were measured for FeAl2O4 and FeCr2O4 by different authors, we performed new measurements on these spinel s. The results on FeAl2O4, showed that the statistical distribution of anot her kind of ions in the positions A may influence the electric field gradie nt at the Fe2+ ions in the tetrahedral interstices. In FeCr2O4 and in the m ixed Fe0.5Mg0.5Cr2O4, the electric field gradient exists at the Fe2+ ions a t room temperature indicating that the degeneracy of the orbital doublet of the Fe2+ is removed.