The transient plane-source technique was used for the simultaneous measurement of thermal conductivity and diffusivity in this system, starting near to 300K. Samples containing 100, 77.5 or 50%Li2SO4 behaved differently to pure Na2SO4. The diffusivity began to increase rapidly at about 640K, while the crystal structure remained monoclinic for Li2SO4 and trigonal for LiNaSO4. In the case of pure Li2SO4, there was an additional discontinuous increase at the structural transition from monoclinic to face-centered cubic at 850K. The diffusivity in Na2SO4 decreased over the entire studied temperature range, which encompassed phase transitions at 474 and 520K. The high-temperature phases, face-centered cubic Li2SO4 and body-centered cubic LiNaSO4 were solid electrolytes, but it was characteristic of these phases that a coupled rotation-like motion of the sulphate ions should enhance cation migration.

Heat Transfer and Ion Migration in the System Li2SO4-Na2SO4. B.M.Suleiman, A.Lunden, E.Karawacki: Solid State Ionics, 2000, 136-137, 325-30