Thermal analysis for LiNaSO4 single crystals by differential scanning calorimetry had shown a clear endothermic peak at 796.9K. The enthalpy energy of the structural phase transition, ΔH = 11.94kJ/mol, was measured. The corresponding entropy change, ΔS was 14.98J/Kmol. The dielectric response of LiNaSO4 single crystal under ac electric field was investigated by impedance spectroscopy. Two distinct relaxations in the sample crystal were detected: dielectric dipolar relaxation and ionic conductivity relaxation. The dipolar relaxation peak due to SO4− reorientation was found at around 1.5 x 105Hz, which was temperature independent. The ionic conductivity relaxation due to Li+ was found at the lower frequency and it was temperature dependent. The dc conductivity varied from 6.7 x 10−8S/cm at 423K to 1.0 x 10−4S/cm at above 793K. The activation enthalpy of Li+ was 1.63eV in the temperature range between 593 and 793K. The sample crystal became a fast ionic conductor in the high-temperature phase with the activation energy of 0.08eV. The ionic conductivity and dipolar relaxations were synchronized in the high-temperature phase of the sample crystal.

Ionic Conductivity and Dielectric Relaxation Studies of LiNaSO4 Single Crystal. R.H.Chen, C.M.Tseng, C.S.Shern, T.Fukami: Solid State Ionics, 2010, 181[19-20], 877-82