Native Defects and their Doping Response in the Lithium Solid Electrolyte Li₇La₃Zr₂O₁₂

The Li-stuffed garnets Li _xM ₂M3′O ₁₂ are promising Li-ion solid electrolytes with potential use in solid-state batteries. One strategy for optimizing ionic conductivities in these materials is to tune lithium stoichiometries through aliovalent doping, which is often assumed to produce proportionate numbers of charge-compensating Li vacancies. The native defect chemistry of the Li-stuffed garnets and their response to doping, however, are not well understood, and it is unknown to what degree a simple vacancy-compensation model is valid. Here, we report hybrid density functional theory calculations of a broad range of native defects in the prototypical Li garnet Li ₇La ₃Zr ₂O ₁₂. We calculate equilibrium defect concentrations as a function of synthesis conditions and model the response of these defect populations to extrinsic doping. We predict a rich defect chemistry that includes Li and O vacancies and interstitials, and significant numbers of cation-antisite defects. Under reducing conditions, O vacancies act as color centers by trapping electrons. We find that supervalent (donor) doping does not produce charge compensating Li vacancies under all synthesis conditions; under Li-rich/Zr-poor conditions the dominant compensating defects are Li _Zr antisites, and Li stoichiometries strongly deviate from those predicted by simple "vacancy compensation" models.