The effect of firing temperature, preparation technique and composition on the electrical properties of the nickel cobalt oxide series NixCo1-xOy

The spinel NiCo2O4 and the materials within the Ni-Co oxide series have well established applications in electrochemistry. However, the importance of the electrical conductivity of these materials and the consequences of the choice of preparation technique and firing regime are often overlooked. In this paper the effect of thermal treatment on the formation of the NiCo2O4 phase, its structure and electrical properties are investigated. Given the selection of an appropriate firing regime, a range of preparation techniques (thermal decomposition, cryochemical, spray pyrolysis and several precipitation methods) are investigated for the resultant electrical, structural and morphological properties. Finally, having selected an appropriate preparation procedure, the entire range of Ni-Co compositions is investigated with respect to the phases formed and their electrical properties. The formation of pure NiCo2O4 in a narrow range of firing temperatures is highlighted and the temperature of 375degreesC is identified as being the most suitable. Besides morphological and granular concerns regarding the selection of the preparation procedure, the importance of the formation of the NiCo2O4 phase for the attainment of high electrical conductance is illustrated. Furthermore, the existence of the NiCo2O4 phase in compositions considerably outside of this stoichiometry is noted, and the presence of this phase in the attainment of high electrical conduction is highlighted. (C) 2004 Kluwer Academic Publishers.