Synthesis-Controlled Polymorphism and Anion Solubility in the Sodium-Ion Conductor Na3InCl6-xBrx (0 ≤ x ≤ 2)

Zhao, Tong; Kraft, Marvin A.; Zeier, Wolfgang G.

Abstract

Motivated by the significant transport property improvement of the anion-substituted lithium metal halides, a series of anion mixed solid solutions of Na3InCl6-xBrx (0 ≤ x ≤ 2) are successfully synthesized by ball milling and subsequent annealing. By milling, the Na3InCl6-xBrx solid solution series crystallizes in a monoclinic P21/n phase, while the subsequently annealed Na3InCl6-xBrx series transforms into a trigonal P3̅1c phase. Through annealing and changes of the structure type, greater anion solubility can be achieved. The halide substitution slightly improves the ionic conductivity in the Na3InCl6-xBrx series, indicating that mixed halide compositions and their structural changes affect the ionic transport albeit less strongly than in the lithium analogues such as Li3YCl6-xBrx and Li3InCl6-xBrx