Fine powders and film samples were treated with the Lewis acids, SbF3 and BF3, in order to draw F- ions out of the boundary regions. The conductivity data indicated that there was a significant enhancement of the ionic conductivity, with a slope that was characteristic of F--vacancy migration. It was noted that simple homogeneous doping by Sb and B would lead to conduction via interstitials, and therefore to a different activation energy. The enhancement was not due to O impurities that were introduced by the heat-treatment. This was proved by preparing the samples in various gaseous atmospheres. A quantitative estimation of the enhanced conductivity was presented which took account of space-charge effects. Conductivity results for thin films also confirmed the assumed existence of space-charge regions, due to the attractive force of the adsorbed Lewis acid.

Y.Saito, J.Maier: Journal of the Electrochemical Society, 1995, 142[9], 3078-83