These Na-rich NASICON-type ceramics were investigated in order to obtain a material which had a high Na conductivity and a high density. It was found that the ionic conductivity and the sinterability were greatly improved by increasing the Na2O contents of the systems. The added Na2O was insoluble in the NASICON-type skeleton, but it acted as a flux for obtaining highly dense ceramics and highly conductive grain boundaries. Partial A2 site insertion by Na+ ions was effective in enhancing conductivity because the conductivity of Na1.5M(III)0.5Zr1.5(PO4)3 (where M was In or Y) was about an order of magnitude higher than the maximum conductivity of the Zr2Na(PO4)3-Na2O system.

H.Aono, E.Sugimoto: Journal of the American Ceramic Society, 1996, 79[10], 2786-8