Effect of Y substitution for Nb in Li5La3Nb2O12 on Li ion conductivity of garnet-type solid electrolytes

► Y-doped Li5La3Nb2−xYxO12−δ as fast solid Li ion electrolytes. ► 7Li NMR shows a sharp peak at 0 ppm and is due to fast migration of Li ions. ► AC impedance shows mainly bulk contribution to the total conductivity. ► Unlike Sb and Te substitution, the doping of Y restored the ionic conductivity.