Composites which contained 25vol% of Teflon were prepared in order to study the effect of a phase transition upon Li+ conduction. The composite consisted of aggregates of Sn2Li(PO4)3 particles which were surrounded by Teflon regions that acted as a skeleton. The imaginary part of the electric modulus exhibited 2 peaks, at high and low frequency, which were attributed to the responses of the grain and of the grain boundary. The ionic conductivity within the grains of both phases was some 3 orders of magnitude larger than that found for the grain boundary. It was noted that the activation energy for the grain interior decreased from 0.68eV for the low-temperature phase, to 0.34eV for the high-temperature phase. The activation energy for Li+ movement through the grain boundaries increased from 0.45 to 0.56eV. An anomalous increase in the activation energy for the grain-interior response of the high-temperature phase was found to occur before the latter transformed into the low-temperature phase.

A.Martinez-Juarez, R.Jimenez, P.Duran-Martin, J.Ibañez, J.M.Rojo: Journal of Physics - Condensed Matter, 1997, 9[20], 4119-28