Preparation conditions of pure and stoichiometric NixFe3-xO4 bulk ceramics

The NixFe3-xO4 (0 < X < 1) phases are spinels which are difficult to obtain under pure, dense and conductive ceramics forms. Treatment under inert atmosphere leads to a biphasic system of spinel and NiO monoxide. Treatment under air does not allow obtaining an optimised conductive ceramic because of oxidation during the cooling or quenching. Then, two step processes is proposed to obtain pure and stoichiometric nickel ferrites. At first, a treatment under air is carried out to synthesise dense and pure spinel ceramics. This treatment is followed by an annealing under inert atmosphere to reduce a part of Fe3+ and to form stoichiometric ferrites with semiconducting properties. (C) 2004 Elsevier SAS. All rights reserved.