Synthesis and thermal behavior of Fe3O2(BO4) oxoborate

Iron oxoborate Fe3O2(BO4) has been first produced in solid-phase chemical reactions. Its thermal behavior in the temperature range 20-900A degrees C is studied with the use in-situ high-temperature powder X-ray diffraction. It is shown that Fe3O2(BO4) begins decomposing with the formation of Fe2O3 in the temperature range 660-900A degrees C. Thermal expansion is sharply anisotropic at room temperature (alpha(max)/alpha(min) = 7) and becomes more isotropic with an increase in the temperature (alpha(max)/alpha(min) = 1.2). The degree of oxidation of Fe3+ has been confirmed by Mossbauer spectroscopy (at a room temperature), and two nonequivalent positions in the structure have been detected, which are occupied by iron atoms with the octahedral environment of the oxygen atoms.