Fine CaF2 powders and films were treated with SbF5 and BF3 in order to draw F- ions out of the boundary regions. The conductivity data for polycrystalline ceramics which had been treated in this way revealed a significant enhancement of the ionic conductivity, with a slope that was characteristic of F- vacancy migration. After the above treatment, the impedance spectra of film samples exhibited 2 semi-circles. The high-frequency arc was attributed to bulk conductivity, plus interfacial contributions in parallel with the bulk pathway. The low-frequency semi-circle was attributed to a blocking effect that was due the grain boundary core structure. A prediction of the increased conduction, which was based upon space-charge effects, agreed satisfactorily with the experimental results.

Y.Saito, J.Maier: Solid State Ionics, 1996, 86-88[1], 581-4