EVIDENCE OF MONODIMENSIONAL CLUSTERS IN SOME FLUORITE-TYPE ANION-EXCESS SOLID-SOLUTIONS - CORRELATION BETWEEN VACANCIES AND INTERSTITIAL FLUORINE ANIONS

The formation of two-file monodimensional 2n: 2: 3n 2 and 2n: 2: 4n: 2 clusters is proposed to account for the fluorine ion conductivity of the Pb1-xInxF2 + x and Pb1 - xZrxF2 + 2x solid solutions on hand of a structural correlation model. The clusters are based on the association of 2n + 2 vacancies in the normal positions of the fluorite-type structure with 3n (or 4n) F′ and 2F″ interstitial anions, they are compared with the single-file monodimensional cluster n + 1: 2n: 1 found for the analogous Pb1 - xBixF2 + x series. Correlations are established on one hand between interstitial F′ ions and vacancies within clusters, on the other hand between interstitial F″ ions and vacancies located on the cluster boundaries. The electrical properties are discussed as a function of concerned clusters for the materials of highest performance in each solid solution. © 1990.