Crystallochemical model of ion-transport percolation in nonstoichiometric M1-xRxF2+x phases with the defect CaF2-type structure

A crystallochemical model of ion-transport percolation in M1-xRxF2+x (M = C a, Sr, Ba; R = RE) solid solutions with the "defect" CaF2-type structure ha s been suggested. Within this model, the percolation thresholds in M1-xRxF2 +x crystals with tetrahedral R4F26- and octahedral R6F37-clusters are consi dered, whose existence is highly probable in these disordered fluorite phas es. It is established that the calculated percolation thresholds x(c) = 2.8 mol % for nnn (next nearest neighbors) [(R6F37)(M5F32)-F-i] and x(c) = 4.7 mol % for nn (nearest neighbor) [(R4F76)(M6F32)-F-i] are in satisfactory a ccord with the experimental percolation thresholds determined from the cond uctometric data. (C) 2000 MAIK "Nauka/Interperiodica".