Correlation among crystal and local structure, phase transition, and Li–ion conduction of solid electrolyte Li7La3Zr2O12

Abstract

The correlation among the crystal and local structure, phase transition, and Li–ion conduction of the solid electrolyte Li7La3Zr2O12 (LLZ) was investigated by quantum beam technique. According to the results of Rietveld refinement using Neutron diffraction data, the Li (8a) and Li (16f) sites have the deficiency of approximately 3∼5% in LLZ. These results of Li site occupancies were adopted to the Rietveld refinements with in situ Synchrotron X–ray Diffraction's (SR–XRD) from 300 K to 1000 K. The phase transition from the tetragonal to cubic phase was observed in in situ SR–XRD. The results of Rietveld refinements with in situ SR–XRD showed the coexistence of the tetragonal and cubic phase from 860 K to 880 K. The Li–ion conduction was discussed with respect to the atomic displacement parameters, electric density estimated by Rietveld refinements and Maximum Entropy Method (MEM) analysis, and local structure estimated by X–ray Absorption Spectra (XAS) and Pair Distribution Function (PDF) analysis. The Li–ion diffusion mechanism was discussed with crystal and local structures at high temperatures of LLZ. In particular, the coexistence of tetragonal phase at the phase transition, the bond of the Li and oxide at tetragonal phase, and the low symmetry of ZrO6 up to about 930 K are thought to inhibit Li diffusion.