Synthesis and characterization of Fe-Ga mixed hydroxide powders

Several samples of iron gallium mixed oxyhydroxides with stoichiometry Fe1-xGax (with x = 0, 0,10, 0.25, 0.50, 0.75, 0.90) have been synthesized by a coprecipitation method. They have been characterised from the point of view of their solid state structure by X-ray diffraction (XRD), thermogravimetry and differential thermal analyses (TG-DTA), FTIR and diffuse reflectance (DR) UV-VIS spectroscopy. After drying at 393 K, only one crystalline phase denoted as alpha-(Fe,Ga)OOH, is found in the samples, ie. a solid solution in the whole composition range in agreement with the continuous lowering of the unit cell parameter. When Ga is added in small amounts to FeOOH, it tends to notably hinder alpha-(Fe,Ga)OOH crystallisation. The electronic spectra suggest that clustering of Fe3+ in dilute samples may occur. Low-temperature thermal decomposition of such mixed oxyhydroxides gives rise to corundum-hematite type solid solutions in the whole compositional range.