The conductivities of a series of fluorite-type solid-solutions, Pb1-xYxF2+x (x = 0.007 to 0.222), were measured under vacuum at 100Hz to 3MHz and 25 to 250C. It was found that the conductivity decreased, and the activation energy increased gradually, upon increasing the Y-content up to about 4.5mol% of Y3+. Between this value and 22mol%Y3+, the conductivity increased and the activation energy decreased. That is, 2 distinct composition regions could be delineated. In one of them, the polarizability factor predominated over the number of extra-interstitial F anions. The opposite was true in the other region. This reflected a competition between the disorder caused by interstitial F anions, and the polarizability of the host and added cations.

Ionic Conductivity in Solid Solutions of PbF2 and YF3. S.J.Patwe, P.Balaya, P.S.Goyal, A.K.Tyagi: Materials Research Bulletin, 2001, 36[9], 1743-9