Solid Phase Transitions and Fast Ion Transport in LiNaSO 4: LiCl: Na 2WO 4 Mixed Systems

LiNaSO 4:LiCl:Na 2WO 4 composites of a few different compositions have been prepared by quenching the melt and studied for the first time with a view to improve the ionic conductivity of LiNaSO 4 at the lowest possible temperature. The phase formations of the composites have been analyzed by means of X-ray powder diffraction technique. The transport properties have been studied by DSC and complex ac impedance analysis (to extract the dc electrical conductivity, σ dc). The X-ray diffractograms show evidence for solid solutions (ss) as well as a second dispersed phase due to undissolved excess compound (LiCl). The σ enhancement may be attributed to the increase in interfacial conductivity due to the increase in concentration of the charge carriers (ions or vacancies) forming a diffuse space charge layer between the two ion conductors, i.e., the solid solution of LiNaSO 4 with dissolved chloride and tungstate fractions and a chloride phase with dissolved sulfate fraction. DSC measurements show improved thermal properties with respect to α-LiNaSO 4. The present composite mixtures offer the choice of lower transition temperatures, but these are accompanied by lower transition enthalpies.