IONIC-CONDUCTIVITY AND SINTERABILITY OF NASICON-TYPE CERAMICS - THE SYSTEMS NAM(2)(PO4)(3)+YNA(2)O (M=GE, TI, HF, AND ZR)

Sodium-rich NASICON-type ceramics, the NaM(2)(PO4)(3) + yNa(2)O (M = G e, Ti, Hf, Zr) systems, were investigated in order to obtain a materia l having a high Na+ conductivity and high density, The ionic conductiv ity and the sinterability were greatly improved by an increase in the value off for all of the systems examined. Added Na2O was not soluble in the NASICON-type skeleton, since the lattice constants and the X-ra y diffraction patterns were not changed by the Na2O addition in all of the samples, Na2O acts as a flux for obtaining highly dense ceramics and highly conductive grain boundaries. Partial A(2) site insertion by Na+ ions is effective for the enhancement of conductivity, because th e conductivity for Na(1.5)M(III)(0.5)Zr-1.5(PO4)(3) (M = In or Y) is a bout 1 order of magnitude higher than the maximum conductivity of the NaZr2(PO4)(3) + yNa(2)O system.