CHARACTERIZATION OF THE MIXED-VALENT TL-1222 FERRITE TLSR4FE2O9-DELTA

The mixed valent Tl-1222 ferrite TlSr4Fe2O9 has been prepared and characterized using various techniques. Its structural features as well as chemical analyses evidenced that this compound shows some non-stoichiometry and that it can be formulated Tl0.96Sr4Fe2O8.70. Magnetic measurements as well as Mossbauer spectroscopy data agree well with this formulation and have been interpreted on the basis of a temperature dependent mixture of trivalent iron and of a mixed valent iron; it results from a fast electron hopping from site to site whose number increases with temperature even though a complete delocalization is not reached. On account of the Mossbauer results, a charge transfer from oxygen to iron has been assumed at increasing temperature. These peculiar electronic configurations of iron cations result from the presence of thallium cations in a 2D-type material.