19F NMR Investigation of Quenched Sr 1- xBi xF 2+ x Solid Solutions: Correlations between Short Range Ordering and Ionic Conductivity

Abstract

A 19F NMR investigation of fluorite-type Sr 1- x Bi x F 2+ x solid solutions (0 ≤ x ≤ 0.50) has been carried out on samples quenched from 700°C. The interpretation of the NMR signal is based on the existence of different fluoride ion sublattices and partial exchange between them at increasing temperature. The NMR study confirms the validity of the clustering process proposed for Sr 1- x Bi x F 2+ x on the basis of electrical conductivity and neutron diffraction results; i.e., progressive transformation with rising x of 3:2:3:0 into 1:0:3:0 clusters. Furthermore, the 19F NMR investigation has made it possible to show that the interstitial fluorine anions of F′ type ( 1 2 , u, u : u ≃ 0.37) are responsible for the long range motions in Sr 1- x Bi x F 2+ x .