Effect of MgO addition on the ionic conductivity of LiGe2(PO4)3 ceramics

Effect of the addition of MgO, along with Li2O, as sintering aid on the densification and ionic conductivity of Li-analogues of Nasicon has been studied. For this purpose, a series of compounds, LiGe2(PO4)3 (LGP)+x(MgO)+y(Li2O), x=y=0–0.7; x=0.2, 0.5 and y=0; x=0 and y=0.2, 0.5 and Li1.4[Ge1.6Al0.4](PO4)3 (LAGP)+x(MgO)+x(Li2O), x=0–0.3, have been synthesized and characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy (XPS), density, porosity and microstructure (by scanning electron microscope, SEM) of the sintered pellets. Results show that the additives do not get incorporated in to the crystal lattice of the Nasicon but act as a binder and drastically reduce the porosity of the pellets and improve connectivity between the grains. Binder addition enhances the ionic conductivity (σionic: bulk, σB and total, σT) at any given temperature in the LGP series and the σT reaches 1.2×10−4 S cm−1 at 100 °C in LGP 5, which is three orders of magnitude higher than that shown by LGP 0 at the same temperature. Similar enhancement of σB is also seen. However, the respective energies of activation, Ea(T) and Ea(B) behave differently with the binder addition. The LAGP series also show an enhancement of σT with the binder addition, by a factor of two and the Ea(T) remains almost unchanged. Present study shows that MgO acts as a binder and helps in reducing the porosity and improving the σionic of the Li-Nasicon phases.