Ionic Conductivity and Sinterability of NASICON‐Type Ceramics: The Systems NaM 2 (PO 4 ) 3 + y Na 2 o (M = Ge, Ti, Hf, and Zr)

Sodium‐rich NASOCON‐type ceramics, the NaM 2 (PO 4 ) 3 + y Na 2 O (M = Ge, Ti, Hf, Zr) system, were investigated in order to obtain a material having a high Na + conductivity and high density. The ionic conductivity and the sinterability were greately improved by an increase in the valve of y for all of the system examined. Added Na 2 O was not souble in teh NASICON‐type skeletton, sice the lattice constants and teh X‐ray diffraction patterns were not changed by the Na 2 O addintion in all of the samples. Na 2 O 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 the conductivity for Na 1.5 M(III) 0.5 Zr 1.5 (PO 4 ) 3 (M = In or Y) is about 1 order of magnitude higher than the maximum conductivity of the NaZr 2 (PO 4 ) 3 + y Na 2 O system.