) Nb and Ta Doping: Nb and Ta show an almost exclusive preference for Zr sites, Figures ) and (e), with formation energies of ∼ 0.80 eV and ∼ 0.59 eV, respectively and is in agreement with previous DFT studies. Nb(Ta) •• La possess formation energies ∼ 3.5 eV higher than Nb(Ta) Zr at E F . The formation energy for Nb • Zr is about 0.2 eV higher than Ta • Zr implying a higher solubility of Ta than Nb in LLZO. Similar to Al and Ga, Nb and Ta will be charge compensated by the formation of additional V ′ Li , equation 11.