Electrical and thermal properties of polycrystalline Li2SO4 and Ag2SO4

The electrical conductivities (sigma) of polycrystalline Li2SO4 and Ag2SO4 are investigated in the temperature ranges 310-950 and 370-730 K, respectively. An increase in the magnitude of sigma followed by a change in the slope of In sigma T against T-1 plots is observed around 860 and 714 K for Li2SO4 and Ag2SO4, respectively, which correspond to the phase transition temperatures (T-p) from the normal ionic solid (alpha-phase) to the superionic conducting phase (beta-phase). The activation enthalpies of the superionic phase and the enthalpies of formation of defects and association were evaluated and discussed from the temperature variation of sigma. The specific heat capacity (C-p), total thermal conductivity (lambda(t)) and thermal diffusivity (a) were measured for polycrystalline Li2SO4 and Ag2SO4 in the temperature range 290-635 K. The radiative pulse heat technique was used for the measured thermal properties. The results indicated that the mechanism of heat transfer is due mainly to phonons. The roles of photons and bipolars are negligible in the investigated temperature range. (C) 1998 Elsevier Science Ltd. All rights reserved.