It was noted that these ceramics exhibited a lower phase transition temperature and a higher ionic conductivity, at low to moderate temperatures, than those of Li2SO4. The ionic conductivity ranged from 0.001 to 0.01S/cm for the low-temperature phase of the present ceramics, and was considerably higher than that of Li2SO4. The conductivity of the high-temperature phase was between 0.1 and 1S/cm at temperatures above 460C. The materials were not simply 2-phase mixtures, and high-temperature powder X-ray diffraction data showed that samples which contained 57mol%Li2SO4 had a different crystal structure to that of samples with a higher content. The highest ionic conductivity values were obtained in this intermediate composition range. Scanning electron microscopy and conductivity results showed that the highest conductivity was found for samples with the smallest grain size. The ceramics were good conductors of both Li+ and H+ ions. In H-containing atmospheres, proton conduction predominated in the low-temperature phase. In the high-temperature phase, the proton conductivity was 1 to 2 orders of magnitude lower than that due to Li+ cations.

B.Zhu, Z.H.Lai, B.E.Mellander: Solid State Ionics, 1994, 70-71, 125-9