High Ionic Conductor Member of Garnet-Type Oxide Li6.5La3Zr1.5Ta0.5O12

Single-crystal rods of Li6.5La3Zr1.5Ta0.5O12 were grown by floating zone melting. The typical size of the single-crystal rod was 8 mm in diameter and 70 mm in length. Li6.5La3Zr1.5Ta0.5O12 crystallizes in a cubic structure with an Ia-3d space group and the lattice parameter a = 12.9455 (6) angstrom. The crystal structure of Li6.5La3Zr1.5Ta0.5O12 was refined to the conventional values of R = 3.32% and wR = 4.45% using single-crystal X-ray diffraction data, and to R = 8.82% and wR = 7.45% using single-crystal neutron diffraction data. Li-ions in the crystal structure occupied two crystallographic sites: the distorted tetrahedral 96 h site and the distorted octahedral 96 h site. Analyzing the results of AC impedance measurements, we estimated the total Li-ion conductivity of member in Li6.5La3Zr1.5Ta0.5O12 to be 1.27x10(-3)Scm(-1) at 298 K. This value is the highest in the reported Li6.5La3Zr1.5Ta0.5O12 members. Using NMR spectroscopy, we determined the Li diffusion coefficient to be 1.57x10(-13)m(2)s(-1) at 298 K and 7.96x10(-13)m(2)s(-1) at 333 K. These values related to Li-ion migration are higher than those reported for polycrystalline samples.