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 20–900°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 660–900°C. Thermal expansion is sharply anisotropic at room temperature (αmax/αmin = 7) and becomes more isotropic with an increase in the temperature (αmax/αmin = 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.