Method for producing halide

A production method for producing a halide, the method includes a heat treatment step of heat-treating a mixed material containing (NH)Yα, (NH)Gdβ, Liγ, and Caδin an inert gas atmosphere, wherein α, β, γ, and δ are each independently at least one selected from the group consisting of F, Cl, Br, and I, and the formulas: 0≤a≤3, 0≤b≤3, and 0