The transport properties of super-ionic conductors with a tysonite-type structure were investigated by using impedance spectroscopic, 19F nuclear magnetic resonance, hydrostatic pressure and 36Cl radiotracer techniques. It was demonstrated that these methods could clarify ionic processes at the microscopic level in solid electrolytes with a predominant F mobility. Because ion transport in LaF3 resulted from F- vacancies, an enhancement of ionic conductivity upon replacing La3+ by Sr2+ was expected. It was found that the number of F ion vacancies increased with MF2 substitution. The conductivity was decreased upon adding a tetravalent dopant. In this case, the increase in the concentration of La ion vacancies caused a decrease in the extrinsic concentration of F ion vacancies; and therefore a decrease in conductivity. The compositional dependence of the properties of La1-xSrxF3 (where x was between 0 and 0.16) exhibited a conductivity maximum in the case of La0.95Sr0.05F2.95. This maximum was attributed to a so-called percolation mechanism in concentrated solid solutions.

I.V.Murin, F.Fujara, O.V.Glumov, A.F.Privalov, H.M.Vieth: Materials Science Forum, 1997, 239-241, 407-12