Synthesis and microstructural properties of mixed iron-gallium oxides

Various mixed Fe-Ga oxides were prepared by the calcination of mixed Fe-Ga oxyhydroxide precursors (α-Fe1−xGaxOOH solid solutions, 0 ⩽ x ⩽ 1) at 500 or 1000 °C. Isostructural corundum-type oxides α-Fe2O3 and α-Ga2O3, as well as their solid solutions α-Fe2−xGaxO3 in the entire concentration range (x = 0, 0.4, 1, 1.6 and 2) were prepared by calcination at 500 °C. An increase in the Ga content in α-Fe2−xGaxO3 resulted in a reduction of the unit cell size, a weakened hyperfine magnetic field, a disappearance of the Morin transition, an increase of magnetization at low temperatures, a shift in the position of IR bands to higher wavenumbers, and a lower intensity of absorption bands in the UV-Vis-NIR spectra. The calcination of Fe-Ga oxyhydroxides at 1000 °C resulted in the formation of a rhombohedral α-Fe2−xGaxO3 phase for x = 0 and 0.4. An orthorhombic GaFeO3 phase with Fe3+ cations located in 3 different octahedral sites was obtained by the calcination at 1000 °C of mixed Fe-Ga oxyhydroxide with the Fe:Ga ratio of 1:1. A monoclinic phase β-Fe2−xGaxO3 (x = 1.6 and 2) was obtained by the calcination at 1000 °C of Fe-Ga oxyhydroxides with 80 and 100 mol% Ga. The monoclinic β-Ga1.6Fe0.4O3 showed two strong luminescence peaks in the blue region of the PL spectrum.