The distribution of the probability density function (pdf) for the sample quenched from 970 K (970Q) shows more anharmonicity than that for the slowly cooled sample (SC) and is spreading out along the [111] directions towards the center of the elementary cell, and the one particle potential of fluorine ion in 970Q is less steep than that in SC towards the unoccupied center. The fact is correlated to the results of the conductivity measurements reported in 1985 by Ito et al.