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Synthesis and microstructural properties of α-Fe1-xGaxOOH solid solutions

Iron oxyhydroxide goethite (α-FeOOH) is wellknown for the ability to incorporate various metal cations in its structure, which has been observed in numerous natural and synthetic samples. αFeOOH doped with various metal cations is commonly used for the preparation of doped αFe2O3 by simple thermal treatment. Although Fe3+ and Ga3+ ions have a great potential for the formation of mixed oxyhydroxides due to the same charge, similar ionic radius and existence of the isostructural oxyhydroxides (α-FeOOH and αGaOOH), only a few studies concerning the solid solutions between α-FeOOH and α-GaOOH have been reported. In the present work α-Fe1-xGaxOOH solid solutions were prepared in the whole Ga:Fe ratio range by precipitation from mixed FeCl3-GaCl3 solutions in the weakly alkaline medium using an organic alkali tetramethylammonium hydroxide (TMAH) for the pH adjustment. Lath-shaped α-Fe1-xGaxOOH particles common for goethite were observed in all samples containing more Fe than Ga, whereas fairly uniform ellipsoidal α-Fe1-xGaxOOH particles characteristic for α-GaOOH formed in alkaline media were observed in samples containing more Ga than Fe. Increase in the content of Ga3+ ions in the α-Fe1-xGaxOOH influenced a decrease in the unit-cell size (in line with lower radius of Ga3+ ions), a reduction of hyperfine magnetic field and collapse of room temperature magnetic order for x > 0.2, a shift in the position of (Fe, Ga)-O-H bending bands and Fe-O and Fe-OH stretching (lattice vibration) bands towards higher wave numbers, a decrease in intensity of all absorption bands in UV-Vis-NIR spectra and shift of Fe3+ ligand field transition bands to higher wave lengths and an increase in dehydroxilation temperature.

α-Fe1-xGaxOOH; synthesis; microstructure; FE-SEM; UV-Vis-NIR; Mossbauer spectroscopy

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