We have successfully synthesized a high-purity polycrystalline sample of tetragonal Li 7 La 3 Zr 2 O 12 . Single crystals have been also grown by a flux method. The single-crystal X-ray diffraction analysis verifies that tetragonal Li 7 La 3 Zr 2 O 12 has the garnet-related type structure with a space group of I4 1 /acd (no. 142). The lattice constants are a ΒΌ 13.134(4) A Λand c ΒΌ 12.663(8) A Λ. The garnet-type framework structure is composed of two types of dodecahedral LaO 8 and octahedral ZrO 6 . Li atoms occupy three crystallographic sites in the interstices of this framework structure, where Li(1), Li(2), and Li(3) atoms are located at the tetrahedral 8a site and the distorted octahedral 16f and 32g sites, respectively. The structure is also investigated by the Rietveld method with X-ray and neutron powder diffraction data. These diffraction patterns are identified as the tetragonal Li 7 La 3 Zr 2 O 12 structure determined from the single-crystal data. The present tetragonal Li 7 La 3 Zr 2 O 12 sample exhibits a bulk Li-ion conductivity of s b ΒΌ 1.63 Γ 10 Γ6 S cm Γ1 and grain-boundary Li-ion conductivity of s gb ΒΌ 5.59 Γ 10 Γ7 S cm Γ1 at 300 K.
The activation energy is estimated to be E a ΒΌ 0.54 eV in the temperature range of 300-560 K.