Ionic conductivity in solid solutions of PbF2 and YF3

Ionic conductivity of a series of fluorite-type solid solutions Pb1-xYxF2+x (0.007 less than or equal to x less than or equal to 0.222) has been measu red in the frequency range 100 Hz - 3 MHz and in the temperature range 25-2 50 degreesC under vacuum. The conductivity decreases and the activation ene rgy increases gradually upon increasing the yttrium content up to similar t o4.5 mol % of Y3+ whereas, beyond that and up to 22 mol % of Y3+, the ionic conductivity increases and the activation energy decreases. Thus two disti nct regions in the general composition Pb1-xYxF2+x could be delineated, in one the polarizability factor predominates over the number of extra-interst itial F anions and vice-versa in the other region. These results indicate t he competing effects between the disorder caused by interstitial F anions a nd the polarizability of the host and guest cations, (C) 2001 Elsevier Scie nce Ltd. All rights reserved.