Ionic Conductivity Enhancement of the Fluoride Conductor CaF2 by Grain Boundary Activation Using Lewis Acids

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Abstract
Following the concept of “heterogeneous doping,” fine powder and films were treated with the Lewis acids and to create a strong driving force to draw F− ions out of the boundary regions according to The powder has been vacuum‐treated with and vapor and then processed to pellets. The conductivity results indicate a significant enhancement of the ionic conductivity with a slope that is characteristic for F−‐vacancy migration. A simple homogeneous doping by Sb and B impurities would lead to a conductivity via interstitials and thus to a different activation energy. The enhancement should not be due to oxygen impurities introduced by the heat‐treatment: this is shown by preparation in different gas atmospheres. A quantitative estimation of the enhanced conductivity assuming space‐charge effects is presented. Conductivity results on thin films also confirmed the assumption of space‐charge regions as a consequence of the attractive forces of the adsorbed Lewis acid.

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