Abstract: The problem of instability in polycrystalline ordered double-perovskite Sr2FeMoO6, is presented in this paper. By the X-ray diffraction analysis and the measuring of electrical and magnetic transports, it is indicated that the perovskite structure of the compound is destroyed, and the Sr2FeMoO2 phase is mainly transformed into SrMoO4 phase when the samples are exposed in damp atmosphere for several weeks or immersed in water for several hours. Simultaneously, their electrical and magnetic properties obviously change, and the value of magnetoresistance remarkably reduces and even vanishes at room temperature. A possible micromechanism of the instability and an effective method to avoid the problem of instability are also discussed.

Key words: Ordered double-perovskite, Instability, Electrical and magnetic properties...