Sodium ion transport in NaPO 3–Na 2SO 4 glasses

Abstract

Sodium metaphosphate-based glasses (mol%) (100 − x) NaPO 3– xNa 2SO 4 (0 ≤ x ≤ 25), were prepared by melt quenching technique. The influence of Na 2SO 4 additives on the thermal, physical and structural properties has been interpreted using density, DSC, ultrasonic velocity and FTIR data. The linear decrease in glass transition temperature ( T g) with increase in Na 2SO 4 content indicates decrease in average chain length of the host glass matrix. FTIR data has revealed that Na 2SO 4 has depolymerized the phosphate glass matrix. The temperature-dependent conductivity data of the above glass samples have been obtained using impedance measurement in the temperature range 400–510 K. The σT products for all the glass compositions have obeyed an Arrehenius relationship, exhibiting an activation energy of about 0.70 eV for ion migration. The ionic conductivity of the host glass, NaPO 3 with a value of 1.1 × 10 −6 S cm −1 has been enhanced by one order of magnitude to a value of 9.4 × 10 −6 S cm −1 for the glass with maximum content of Na 2SO 4 at 450 K. Enhancement in the ionic conductivity has been explained on the basis of dissociation of Na 2SO 4, resulting in the enhancement of the charge carrier concentration. Electronic transport number of a value 0.01 determined by the dc polarization technique and ionic transport number of a value 0.94 measured by the emf method indicate the ionic nature of the conducting species.