Effect of Homovalent Anion Doping on the Conductivity and Phase Transitions in Na2SO4

An attempt has been made to understand the effect of doping homovalent anion dopants such as CO2-3, B4O2-7, MoO2-4, and WO2-4 on the conductivity and phase transitions of Na2SO4 by means of XRD, DSC, and impedance measurements. Our studies indicate that the observed conductivity enhancement is largely due to an increase in the free volume in the structure. Apart from the size, the shape and orientational ordering of the dopant ion in the sulfate sublattice seem to influence the activation energy. The structure of the guest anion appears to be one of the major factors determining the phase stabilization of Na2SO4 (I) at low temperatures.