The effect of the structural environment on the Cl− ion conductivity was demonstrated in LaOCl‐based solid electrolytes. By replacing the La3+ site with lower‐valent Mg2+ or Ca2+ ions, the conductivity was enhanced owing to the formation of a Cl− ion vacancy. Despite the same dopant content, the conductivity of La0.8Ca0.2OCl0.8 was considerably greater than La0.8Mg0.2OCl0.8. This enhancement of the conductivity was influenced by the high ionicity of the Cl− ions, which facilitated the weakening of the La‐Cl bond cleavage to conduct inside the lattice. The elongation of the La‐La distance, associated with the Cl− ion conduction, could also cause an increase of the conductivity.

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Iodide ion conduction was demonstrated and quantified.

Highly Br ¹ ion conducting solid electrolytes were developed by replacing La 3+ ion site in LaOBr with lower valent Sr 2+ and Ca 2+ ions to form Br ¹ ion vacancies for Br ¹ ion conduction with suppressing the sample decomposition. By doping two kinds of divalent cations simultaneously into LaOBr lattice, high amount of Br ¹ ion vacancy was successfully introduced compared to the previously reported La 0.9 Sr 0.1 OBr 0.9. Among the samples prepared, the highest Br ¹ ion conductivity was obtained for the La 0.85 Sr 0.10 Ca 0.05 OBr 0.85 solid, which was ca. 5 times higher than that of La 0.9 Sr 0.1 OBr 0.9 .

Bromide (Br −) ion conductivity in the LaOBr-type solid was successfully improved by partial replacement of the La 3+ ion sites in LaOBr with lower valent Zn 2+ and Sr 2+ ion. Here, Zn 2+ ion having high electronegativity was introduced together with Sr 2+ ion to form large number of Br − ion vacancies for Br − ion migration, since higher electronegativity of cation is effective for building a strong bond with the surrounding anions inside the LaOBr lattice. As a result, a high concentration of Br − vacancies was successfully introduced with prohibiting the lattice collapse, and the extraordinary high Br − ion conductivity was obtained for the La 0.80 Sr 0.15 Zn 0.05 OBr 0.80 solid.

Bromide(Br−) ionconductivity in the LaOBr-type solid was successfully improved by partial replacement of the La3+ sites in LaOBr with Zn2+ and Sr2+. By doping Zn2+ having small ionic radius and high electronegativity together with large size of Sr2+into the La3+ sites, high concentration of Br− vacancies were successfully introduced with prohibiting the lattice collapse, and the extraordinaryhighBr− ion conductivity was obtained for the La0.80Sr0.15Zn0.05OBr0.80 solid.