Etude par résonance magnétique des phénomènes diffusifs dans les phases du système NaFBiF 3

Abstract

19F and 23Na wide-line NMR studies are reported on NaBiF 4 and the solid solution Na 1− x Bi x F 1+2 x for x = 0.62 and x = 0.68 in the −100° to +200°C temperature range. No sodium mobility could be detected in NaBiF 4, but the mobility is significant in the solid solution. The fluorine motions are weakly activated (0.28 eV) in NaBiF 4 and result only from short-range motion (correlated motions or reorientations). In the solid solution the concentration of mobile fluoride ions increases with temperature. Compared to the values given by complex impedance measurements, the activation energies in this thermal range (0.18 eV for x = 0.62 and 0.20 eV for x = 0.68) may be correlated with phenomena preceding the long range conductivity which appears at higher temperature.