Synthesis and structure analysis of tetragonal Li 7La 3Zr 2O 12 with the garnet-related type structure

Abstract

We have successfully synthesized a high-purity polycrystalline sample of tetragonal Li 7La 3Zr 2O 12. Single crystals have been also grown by a flux method. The single-crystal X-ray diffraction analysis verifies that tetragonal Li 7La 3Zr 2O 12 has the garnet-related type structure with a space group of I4 1/ acd (no. 142). The lattice constants are a=13.134(4) Å and c=12.663(8) Å. 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 8 a site and the distorted octahedral 16 f and 32 g 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 7La 3Zr 2O 12 structure determined from the single-crystal data. The present tetragonal Li 7La 3Zr 2O 12 sample exhibits a bulk Li-ion conductivity of σ b=1.63×10 −6 S cm −1 and grain-boundary Li-ion conductivity of σ gb=5.59×10 −7 S cm −1 at 300 K. The activation energy is estimated to be E a=0.54 eV in the temperature range of 300–560 K.