Ionic conductivity and dielectric relaxation studies of LiNaSO₄ single crystal

Thermal analysis for LiNaSO₄ single crystals by differential scanning calorimetry (DSC) had shown a clear endothermic peak at 796.9 K. The enthalpy energy of the structural phase transition, ΔH=11.94 kJ/mol, was measured. The corresponding entropy change, ΔS was 14.98 J/K mol. 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 SO^- ₄ reorientation was found at around 1.5 × 10⁵ Hz, which is 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 6.7×10^-8 Ω^-1 cm^-1 at 423 K to 1.0×10^-4 Ω ^-1 cm^-1 at the temperatures above 793 K. The activation enthalpy of Li⁺+ is 1.63 eV in the temperature range between 593 and 793 K. The sample crystal became a fast ionic conductor in the high-temperature phase with the activation energy of 0.08 eV. The ionic conductivity and dipolar relaxations are synchronized in the high-temperature phase of the sample crystal.