NEUTRON-DIFFRACTION INVESTIGATION OF THE BA1-XBIXF2+X SOLID-SOLUTION

Bragg neutron diffraction studies have been carried out on the fluorite-type Ba1-xBixF2+x (0 less-than-or-equal-to x less-than-or-similar-to 0.45) solid solution. Two interstitial sites of F' and F" type have been identified, the distribution of the fluorine atoms between normal and interstitial sites has been determined as a function of substitution rate. A clustering process in Ba1-xBixF2+x has been proposed on the basis of the neutron diffraction and conductivity results, it consists in a progressive transformation with increasing x of 4:4:3:0 clusters into cubooctahedral 8:12:1:0 clusters. Correlations have been established between these results and those obtained from a F-19 NMR investigation which confirms the validity of the clustering process proposed for Ba1-xBixF2+x.