Electrical properties of Ni/YSZ cermets obtained through combustion synthesis

The synthesis of NI/YSZ cermet with controlled microstructural characteristics presents a lot of interest for many solid-state electrochemical applications. These materials are generally obtained by reducing poorly sintered mixtures of YSZ with nickel oxide by hydrogen. We recently proposed an alternative route based on a thermite reaction performed in a combustion regime. This method makes it possible, in one step, to synthesize highly porous cermet, to sinter the ceramic fraction, and to dope it with yttria. Such an approach represents an application of combustion synthesis or the self-propagating high-temperature synthesis (SHS) technique. We present here electrical characteristics of Ni/YSZ cermets produced by this method. The total electronic conductivity shows an unusually smooth percolation threshold. This fact makes it possible to obtain a fairly high electronic conductivity even at relatively low metal Volume fractions. The ceramic fraction shows an excellent degree of sintering and an ionic conductivity not too different from the conductivity of YSZ single crystals with the same composition. (C) 1998 Elsevier Science B.V. All rights reserved.