Optimum lithium-ion conductivity in cubic Li7−xLa3Hf2−xTaxO12

The nominal Li concentration giving a maximum room temperature Li-ion conductivity σLi ≃ 3.45 × 10−4 S cm−1 with an Ea ≃ 0.438 eV in the system Li7−xLa3Hf2−xTaxO12 fired in an alumina crucible at 1130 °C for 48 h occurs in the narrow range of x = 0.45 ± 0.05. The samples were prepared by solid-state reaction and characterized by XRD, SEM, electrochemical impedance spectroscopy and 7Li MAS NMR measurements.

► Members of the Li7−xLa3Hf2−xTaxO12 (x = 0.1–0.6) series were synthesized by conventional solid-state reaction. ► x = 0.45 showed a maximum Li-ion conductivity of 3.45 × 10−4 S cm−1 with an Ea ≃ 0.438 eV. ► The samples were characterized by XRD, SEM, electrochemical impedance spectroscopy and 7Li MAS NMR measurements.