Phase Stability and Electrochemical Performance of La-Site-Doped Li 6 La 3 Zr 0.5 Nb 0.5 Ta 0.5 Hf 0.5 O 12 High-Entropy Garnets

High Resolution Image Download MS PowerPoint Slide We investigate La-site substitution in the high-entropy garnet Li 6 La 3 Zr 0.5 Nb 0.5 Ta 0.5 Hf 0.5 O 12 (LLZNTH) using Ba 2+, Sr 2+, and Sm 3+ to elucidate how dopant governs phase stability, Li-site distribution, and electrochemical behavior. X-ray diffraction shows that Sr 2+ is incorporated homogeneously into the garnet lattice, whereas the larger Ba 2+ and smaller Sm 3+ ions partially exceed the structural tolerance, generating secondary phases. Nevertheless, the Sm-doped composition ( x = 0.05) exhibits the highest room-temperature ionic conductivity (2.7 × 10 –4 S cm –1 ). Neutron powder diffraction reveals that Sm substitution drives a redistribution of Li + from the tetrahedral 24 d sites into the higher-mobility 96 h positions, enhancing the connectivity of the three-dimensional Li-ion migration network. A Sm-doping series ( x = 0.01–0.05) further shows that only sufficiently high Sm levels induce this redistribution, whereas lower concentrations retain Li arrangements similar to the undoped garnet. Critical current density measurements demonstrate that La-site dopants also influence interfacial stability against Li metal, underscoring a trade-off between bulk transport enhancement and mechanical robustness. Collectively, these findings reveal that in high-entropy garnets improved ionic conductivity can originate not only from phase-pure structures but also from targeted modification of the Li sublattice, even when accompanied by secondary phases, offering a compositional design principle for garnet electrolytes.