Exploring Aliovalent Substitutions in the Lithium Halide Superionic Conductor Li_{3- x}In_{1- x}Zr_xCl₆(0 ≤ x ≤ 0.5)

In recent years, ternary halides Li3MX6 (M = Y, Er, In; X = Cl, Br, I) have garnered attention as solid electrolytes due to their wide electrochemical stability window and favorable room-temperature conductivities. In this material class, the influences of iso- or aliovalent substitutions are so far rarely studied in depth, despite this being a common tool for correlating structure and transport properties. In this work, we investigate the impact of Zr substitution on the structure and ionic conductivity of Li3InCl6 (Li3-xIn1-xZrxCl6 with 0 ≤ x ≤ 0.5) using a combination of neutron diffraction, nuclear magnetic resonance, and impedance spectroscopy. The analysis of high-resolution diffraction data shows the presence of an additional tetrahedrally coordinated lithium position together with a cation-site disorder, both of which have not been reported previously for Li3InCl6. This Li+ position and cation disorder lead to the formation of a three-dimensional lithium-ion diffusion channel, instead of the expected two-dimensional diffusion. Upon Zr4+ substitution, the structure exhibits nonuniform volume changes along with an increasing number of vacancies, all of which lead to increasing ionic conductivity in this series of solid solutions.