1Physics Department, Faculty of Science, Alexandria University, Egypt.
2Physics and Chemistry Department, Faculty of Education, Alexandria University, Egypt.
Single crystals of sodium potassium sulphate, NaKSO4, were grown by slow evaporation method from aqueous solution contained equimolar amounts of pure K2SO4 and Na2SO4. The temperature dependance of d. c. conductivity, σ(T), specific heat at constant presure, Cp(T), and spontaneous strain, η(T), have been measured for sodium potassium sulphate, NaKSO4, crystals from 300 to 500 K. Over the temperature range of interest the conductivity exhibited two regimes; intrinsic above Tc and extrinsic below Tc. The thermal expansion coefficients were calculated from dilatometric measurements during heating and cooling and no hysterises phenomena were detected. In the other hand DSC meauserements of Cp showed a pronounced maximum at Tc = 453 K. The correlation between d. c. conductivity σ(T) and specific heat Cp(T) is clear. This behaviour is attributed to the dominating role of the nonlinearity in the temperature dependence of σ and Cp.
