The ionic conductivity of Na2CO3:ABO(3) (where A = Li/K/Ba and B = Nb/Ti) heterogeneous solid electrolyte systems is investigated using the complex impedance spectroscopy. Presence of two depressed semicircular arcs in the complex impedance plane is accounted for the difference in defect concentration and mobility of ion in homo- and hetero-junctions. The enhancement in conductivity is understood to be due to the formation of a space charge layer across the hetero-junction. The optimised composition (30 wt.% LiNbO3, dispersed Na2CO3) is found promising for CO, electrochemical gas sensor application.