Fast cation conductivity by percolation in alkali sulfate compositions
The results of ac electrical conductivity measurements on the compounds Na 2 SO 4 , Ag 2 SO 4 , Li 2 SO 4 and LiNaSO 4 incorporating the isovalent guest ions WO 2 2− , MoO 4 2− , Rb + , K + or the aliovalent guest ions SiO 4 4− , Cd 2+ , Gd 3+ in their respective sublattices are presented. In all cases, except K + , an increase in cation conductivity was observed. The higher cation conductivity is attributed to lattice expansion and/or incorporation of ion vacancies by guest ion presence and structural transformation. The results are interpreted in terms of a percolation-type transport mechanism and cannot be reconciled to the proposed anion-rotation “paddle-wheel” mechanism.