Synthesis-Controlled Cation Solubility in Solid Sodium Ion Conductors Na_2+xZr_1–xIn_xCl₆

Mechanochemically synthesized sodium halide solid solutions with the general formula Na 2+ x Zr 1– x M x Cl 6, as a class of potential catholytes, show promising ionic transport in comparison to their parental materials such as Na 3 YCl 6 . However, the influence of subsequent heat treatment protocols on the structure and transport properties of these materials is still not fully understood. In this work, a series of Na 2+ x Zr 1– x In x Cl 6 solid solutions are prepared by ball milling with subsequent annealing at different temperatures. X-ray diffraction analyses show a full indium solubility in Na 2+ x Zr 1– x In x Cl 6 when synthesized at low temperatures and crystallizing in the P 2 1 / n phase. In contrast, at higher heat treatment temperatures, exsolution is observed as the indium-rich Na 2+ x Zr 1– x In x Cl 6 compound tends to partially transform to the trigonal P 3̅1 c phase. By assessing the ionic conductivity of the differently synthesized Na 2+ x Zr 1– x In x Cl 6 series, we can show the synergistic effect of the Na + /vacancy ratio and crystallinity on sodium ion transport in this class of materials.