Two series of glasses which contained BaF2 and NaF network modifiers, and a third series which contained only NaF, were investigated. The mole fraction of NaF was varied from 0 to 0.45. The alternating-current conductivity was analyzed by using the complex modulus formalism, and a hopping transport mechanism was proposed. The use of 23Na and 19F nuclear magnetic resonance techniques showed that Na+ ions did not act as charge carriers in the conduction mechanism, and that the diffusion process was due only to the motion of mobile F- ions. It was found that the mobility, and the numbers of F- ions which were mobile at the nuclear magnetic resonance time-scale, increased when the BaF2 content was increased. The results indicated the existence of a conductivity minimum, and an activation-energy maximum, at a NaF fraction of 0.30.

J.M.Bobe, J.M.Reau, J.Senegas, M.Poulain: Solid State Ionics, 1995, 82[1-2], 39-52