ION-TRANSPORT IN THE ANION-DEFICIENT NONSTOICHIOMETRIC PHASES LA-0.95(BA1-XSRX)(0.05)F-2.95 0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-1)

The fluoride-ion conductivity of the nonstoichiometric tysonite phases La-0.95(Ba1-xSrx)(0.05)Fe-2.95 (0 less than or equal to x less than o r equal to 1) is investigated by impedance spectroscopy. Electrophysic al measurements are performed in the frequency range 5-5X10(5) Hz and temperature range 300-700 K. A discontinuity is observed in the temper ature dependence of the conductivity at T-c=410 -430 K. The behavior o f the temperature dependence of the electrical conductivity is explain ed within a transport model taking into account the migration of fluor ide ions between different inequivalent structural sites. The maximum value of the conductivity at room temperature (293 K) is 2x10(-4) Omeg a(-1) cm(-1) for the solid solution La0.95Sr0.05F2.95. The fluorine-io n conductivity in La-0.95(Ba1-xSTx)(0.05)F-2.95 Single crystals is alm ost an order of magnitude larger than the value for the commercial sol id electrolyte La0.992Eu0.008F2.992 (a fluorine-selective membrane) ha ving a tysonite structure. (C) 1998 American Institute of Physics.