Topochemical synthesis of cation ordered double perovskite oxynitrides

Topochemical nitridation in ammonia at moderate temperatures of cation ordered Sr₂FeWO₆ produces new antiferromagnetic double perovskite oxynitrides Sr₂FeWO_6-xN_x with 0 < x ≤ 1. Nitrogen introduction induces the oxidation of Fe²⁺ to Fe³⁺ and decreases T_N from 38 K (x = 0) to 13 K for Sr₂FeWO₅N which represents the first example of a double perovskite oxynitride with both high cationic order and nitrogen content. This synthetic approach can be extended to other cation combinations expanding the possibility of new materials in the large group of double perovskites.