Li-ion conductivity and crystal structure of garnet-type Li_6.5La₃M_1.5Ta_0.5O₁₂ (M = Hf, Sn) oxides

Abstract

We investigated the Li-ion conductivity and crystal structure of the Ta-doped Li₇La₃M₂O₁₂ (M = Hf, Sn) samples. All of the Ta-doped samples exhibited a relatively high conductivity of ∼10⁻⁴ S cm⁻¹ at room temperature, and the activation energies of Li_6.5La₃Hf_1.5Ta_0.5O₁₂ and Li_6.5La₃Sn_1.5Ta_0.5O₁₂, which were determined from the Arrhenius plots in measured temperature range, are Ea = 0.400(6) and 0.451(1) eV, respectively. The crystal structure was analyzed by Rietveld method using powder X-ray diffraction data. From a view point of the Li–O polyhedral volume in unit cell, Li_6.5La₃Hf_1.5Ta_0.5O₁₂ has a most suitable Li-ion environment among the Li₇La₃M₂O₁₂ (M = Zr, Hf, Sn) compounds.