METHOD FOR PRODUCING HALIDE

The production method of the present disclosure includes a heat treatment step of heat-treating a material mixture containing a compound containing Y, a compound containing Sm, NH4α, Liβ, and Caγ2 in an inert gas atmosphere. The compound containing Y is at least one selected from the group consisting of Y2O3 and Yδ3, and the compound containing Sm is at least one selected from the group consisting of Sm2O3 and Smε3. The material mixture contains at least one selected from the group consisting of Y2O3 and Sm2O3, and α, β, γ, δ, and ε are each independently at least one selected from the group consisting of F, Cl, Br, and I.