Li1+xAlxGeyTi2-x-y(PO4)3 NASICON Series

Two Li1+xAlxGeyTi2-x-y(PO4)3 (0.2 e x e 0.8; y ) 0.8, 1.0) solid solutions have been prepared as polycrystalline powders. These compounds crystallize in the NASICON-type structure, R3c space group, and the crystal structures have been characterized by the Rietveld method with laboratory X-ray powder diffraction data. The cell parameters evolution along the two series agrees with the substitution of larger Ti 4+ by smaller Ge 4+ and Al 3+ cations. The electrical properties have been characterized by an impedance study. Bulk conductivity values at room temperature are close to 10 -3 S‚cm -1 with low activation energies (0.35 eV). The trajectories of the Li + cations have been simulated from the bond valence sum calculation. Structural keys, which justify the high ionic conductivity and the low activation energy, are discussed.