The nuclear magnetic resonance of 63Cu was investigated, in Cu4RbI2-xCl3+x, for x-values of between 0 and 0.25. It was found that the rapid motion of the Cu ions was thermally activated; with energies ranging from 0.094 to 0.125eV. No sign of a discontinuous change in the activation energy was detected.

H.Looser, D.Brinkmann: Solid State Ionics, 1985, 17[4], 277-80