Effects of penta- and trivalent dopants on structure and conductivity of Li7La3Zr2O12

• MD simulation clarifies dopant distribution in LLZ and their effect on conductivity.
• Al3 + doping on Li 24(d) site creates Li vacancies, but obstructs Li+ pathways.
• Homovalent Ga doping on La sites is not effective in stabilising the cubic phase.
• Cooling-rate dependent Li ordering causes a significant conductivity hysteresis.

Due to their high ionic conductivity and stability versus metallic lithium, garnet-related Li7La3Zr2O12 (LLZ) are of interest as Li+ solid electrolytes. The correlation between structure and ion mobility in undoped, Ta5 +, Nb5 +, Ga3 + or Al3 + doped LLZ is studied combining molecular dynamics (MD) simulations and experimental characterisation. Neutron and in situ XRD powder diffraction are employed to analyse the Li and dopant distribution and temperature dependence of the structure. Pentavalent doping enhances ionic conductivity by increasing the vacancy concentration and reducing local Li ordering. Trivalent doping Al3 + or Ga3 + on the Li site is slightly less effective in enhancing conductivity. Ga3 + doping on the La3 + site only helps to retain the cubic phase, but does not affect the mobile charge carrier concentration. The cooling rate after sintering is found to strongly affect both the ionic conductivity and its hysteresis on subsequent thermal cycling in the low temperature range, which can be attributed to local Li ordering as manifested by non-linear variations of the lattice parameters.