Effect of Rb and Ta Doping on the Ionic Conductivity and Stability of the Garnet Li7+2x–y(La3–xRbx)(Zr2–yTay)O12 (0 ≤ x ≤ 0.375, 0 ≤ y ≤ 1) Superionic Conductor: A First Principles Investigation

In this work, we investigated the effect of Rb and Ta doping on the ionic conductivity and stability of the garnet Li7+2x–y(La3–xRbx)(Zr2–yTay)O12 (0 ≤ x ≤ 0.375, 0 ≤ y ≤ 1) superionic conductor using first principles calculations. Our results indicate that doping does not greatly alter the topology of the migration pathway, but instead acts primarily to change the lithium concentration. The structure with the lowest activation energy and highest room temperature conductivity is Li6.75La3Zr1.75Ta0.25O12 (Ea = 19 meV, σ300K = 1 × 10–2 S cm–1). All Ta-doped structures have significantly higher ionic conductivity than the undoped cubic Li7La3Zr2O12 (c-LLZO, Ea = 24 meV, σ300K = 2 × 10–3 S cm–1). The Rb-doped structure with composition Li7.25La2.875Rb0.125Zr2O12 has a lower activation energy than c-LLZO, but further Rb doping leads to a dramatic decrease in performance. We also examined the effect of changing the lattice parameter at fixed lithium concentration and found that a decrease in the lattice paramet...

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