The defect structure of fluorite-type Ba1−xUxF2+2x solid solutions, which exhibit fast fluoride ion conductivity, has been investigated by quasi-elastic diffuse neutron scattering (QDNS) experiments, and thermally stimulated depolarisation current (TSDC) measurements. A comparison with model calculations reveals (212) clusters to dominate the defect structure. From 10 to 400K TSDS spectra reveal for x <0.05 six relaxation peaks of dipolar nature, along with the relaxation of macroscopic space charge. Conductivity parameters calculated from the latter relaxation compare very well with those obtained from a.c. ionic conductivity studies. The low-temperature relaxation at 29.5 K is ascribed to depolarisation steps of (212) clusters. Evidence for the relaxation of a minor amount of (UBaFi)x dipoles is found. A direct indication of the freedom of orientation of a (212) cluster is obtained from an initial QDNS-study on a polarised crystal.
|Journal||Solid State Ionics|
|Publication status||Published - 1986|