Phase transition and electrical properties of Na 2SO 4

Abstract

The phase transition and electrical properties of undoped and yttrium-doped Na 2SO 4 were studied by differential thermal analysis, X-ray diffraction and electrical conductivity measurement. The high-temperature phase (phase I) was stable above 250°C in undoped Na 2SO 4. An addition of yttrium affected the transition behavior and improved the electrical properties. The solubility limit of yttrium in Na 2SO 4 (phase I) was estimated to be 5 at.% Y. Doping of yttrium less than 1.7 at.% Y lowered the transition temperature to ≈170°C, whereas doping of more than 3.8 at.% Y raised the transition temperature to 320°C. The electrical conductivity of phase I in undoped Na 2SO 4 was 1.5×10 −2 ω − cm − at 800°C and the apparent activation energy was ≈1.43 eV between 640 and 800°C. Doping of yttrium increased the electrical conductivity. The maximum conductivity of 1.6×10 −1 ω −1 cm −1 at 800°C was obtained in the sample containing 3.8 at.% Y with the apparent activation energy of 0.43 eV.