Preparation and characterization of p-type Fe2O3 pellets from Mg doping in pure oxygen atmosphere at high temperatures

In order to prevent the formation of unfavorable Fe3O4 on the surface, an effective way for the preparation of p-type alpha-Fe2O3 pellets by Mg doping (from MgO) in pure oxygen atmosphere between 1173 and 1273 K has been developed. The pellet properties were compared with those prepared in air. The effects of the calcination temperature, holding time during the calcination process, and Mg doping amount have been investigated. The samples were characterized by X-ray diffraction and UV-vis diffuse reflectance for determining the type of iron oxides in the bulk and on the surface. The semiconductor properties were determined by Hall measurement. The results from this research indicate that pure oxygen at 3 atmosphere pressure should be used for suppressing Fe3O4 production on pellet surface. Either 20 h of holding time at 1173 K or 0 h at 1273 K is sufficient for the preparation of p-type alpha-Fe2O3 pellets. Although the higher carrier concentration can be prepared by using more MgO in the pellets, the higher resistivity and the lower electron mobility are the drawbacks. Therefore, only 0.2 at% Mg doped in alpha-Fe2O3 in pure oxygen pressure is suggested for the preparation of p-type semiconductor. (C) 2010 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.