ESTIMATION OF CHARGE-CARRIER CONCENTRATION IN THE FLUORITE-TYPE 2-LESS-THAN-OR-EQUAL-TO-Y-LESS-THAN-OR-EQUAL-TO-X) SOLID-SOLUTION INVOLVING2 SUBSTITUTIONAL CATIONS(X+Y (FIXED X, 0)

The bulk impedance parameters of polycrystalline samples of the Pb1-x- yInx-yBi2yF2+x+y (fixed x, 0 less-than-or-equal-to y less-than-or-equa l-to x) solid solution with fluorite-type structure were determined fr om an analysis of ac conductivity data measured in a wide temperature range. Hopping rates of mobile F- ions were extracted from frequency d ependences of conductivity at different temperatures. The concentratio n of charge carriers in the samples investigated has been estimated. I ndependently of y, its value (log N/cm3, = 21.6 +/- 0.02) allows to pr opose, on the basis of the clustering model, that charge carriers in t hese materials are likely the interstitial fluoride ions of F'' type.