Properties of iron oxides doped with gallium and indium

Iron oxides are widespread compounds in nature and usually contain metal cations other than iron incorporated in their structure [1]. Also, doping of synthetic iron oxides with different metal cations can improve their properties (magnetic, electric, catalytic, photocatalytic, optical, gas sensing, etc) which can be crucial for their applications in advanced technologies. In the present work properties of goethite (α-FeOOH) and hematite (α-F₂0₃) doped with non-magnetic metal cations Ga³⁺ and In³⁺ were investigated. Gallium and indium-doped goethite samples were synthesized by a precipitation method using a strong organic alkali tetramethylammonium hydroxide (TMAH) for pH adjustment [2-4]. Solid solutions of isostructural α-FeOOH and α-GaOOH were prepared in the whole Fe/Ga ratio range (α-Fe_1-xGa_xOOH, 0 < x < 1) [3]. Different iron-gallium oxides were prepared by calcination of α-Fe_1-xGa_xOOH samples at 500 or 1000 grad C [5]. In-doped goethite samples were prepared with maximum In-for-Fe substitution estimated at about 8 mol % [4]. In-doped hematite samples were prepared by calcination of In-doped goethite samples at 500 grad C [6]. Prepared samples were analysed using ⁵⁷Fe Moessbauer spectroscopy and other instrumental techniques. (authors)