Microwave assisted gel-combustion synthesis of 8 mol% YSZ: A study of the effect of fuel on the ionic conductivity

Nano-crystalline 8 mol% yttria stabilized zirconia (YSZ) powders were synthesized by means of microwave-assisted gel combustion process. Three different fuels – citric acid, urea and glycine – were examined for their suitability as the combustion fuel. The combustion synthesis was also carried out by heating using a hot-plate for the purpose of comparing the effect of different type of heat sources on the characteristics of the derived powders. The effect of nature of fuel on the crystal structure, particle size, specific surface area and morphology of the powders was examined. X-ray powder diffraction (XRD), BET gas adsorption technique, dynamic light scattering technique, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and micro-Raman spectroscopy were employed to characterize the powders. Ionic conductivity of the sintered pellets was measured using ac-impedance spectroscopy. The sintered density of compacts obtained from microwave-derived as well as hot-plate derived citric acid–nitrate or glycine–nitrate process was in the range of 94–97% theoretical density (T.D.). However, when urea was used as the fuel, the compacts obtained from the combustion powder yielded density of only ~90% T.D. The activation energies for the conduction of the oxide ions in the sintered pellets obtained from microwave-derived powders using citric acid, glycine and urea as fuels were 1.00, 1.02 and 1.04 eV respectively.