EFFECT OF THE PHASE-TRANSITION OF LISN2(PO4)(3) ON THE LI-TEFLON COMPOSITES( ION CONDUCTION IN LISN2(PO4)(3))

A composite LiSn2(PO4)(3)-25% vol Teflon was prepared to prevent break ages in powder pellets due to the phase transition of LiSn2(PO4)(3) an d, thus, to study the effect of the phase transition on Li+ conduction . The composite microstructure, as followed by scanning electron micro scopy, shows aggregated LiSn2(PO4)(3) particles surrounded by Teflon r egions which operate as a skeleton. The imaginary part of the electric modulus shows two peaks at high and low frequency which are ascribed to grain-interior and grain-boundary response, respectively. In the tw o phases the ionic conductivity inside the grains is about three order s of magnitude larger than that found for the grain boundary. The phas e transition affects the activation energy in different ways. It decre ases for the grain-interior response from 0.68 eV for the low-temperat ure phase to 0.34 eV for the high-temperature phase, while it increase s from 0.45 to 0.56 eV for the Li+ movement through the grain boundari es. An anomalous increase in activation energy for the grain-interior response in the high-temperature phase before it is transformed into t he low-temperature phase has been found.