The effect of adding MgO, together with Li2O, upon the densification and ionic conductivity of Li-analogues of Nasicon was studied. A series of compounds, LiGe2(PO4)3-xMgO-yLi2O (x = y = 0 to 0.7; x = 0.2 or 0.5 and y = 0; x = 0 and y = 0.2 or 0.5) and Li1.4[Ge1.6Al0.4](PO4)3-xMgO-xLi2O (x = 0 to 0.3), were and characterized by means of powder X-ray diffraction, X-ray photo-electron spectroscopy and scanning electron microscopy of the sintered pellets. The results showed that the additives were not incorporated into the crystal lattice, but acted as a binder and sharply reduced the porosity and improved the connectivity between the grains. Binder additions enhanced the ionic conductivity at a given temperature, in the LiGe2(PO4)3 series, and the total conductivity reached 1.2 x 10-4S/cm at 100C. A similar enhancement of the bulk conductivity was observed. The Li1.4[Ge1.6Al0.4](PO4)3 series also exhibited a factor-of-2 enhancement of the total conductivity with binder addition. It was concluded that MgO acted as a binder and improved the ionic conductivity of the Li-Nasicon phases.

Effect of MgO Addition on the Ionic Conductivity of LiGe2(PO4)3 Ceramics. C.J.Leo, G.V.Subba Rao, B.V.R.Chowdari: Solid State Ionics, 2003, 159[3-4], 357-67