Synthesis, Mo-valence state, thermal stability and thermoelectric properties of SrMoO3−xNx (x>1) oxynitride perovskites

Oxynitrides of the general composition SrMoO3−xNx (x>1) were synthesized by thermal ammonolysis of crystalline SrMoO4. According to neutron and X-ray diffraction experiments, the materials crystallize in the cubic perovskite structure (space group Pm3¯m). X-ray absorption spectroscopy (XAS) shows evidence of local distortions of the Mo(O,N)6 octahedra. The oxidation states of Mo determined by X-ray absorption near edge structure (XANES) spectroscopy are slightly lower than that calculated from the oxygen/nitrogen(O/N) content. The disagreement arises from the higher covalence of the Mo–N bonding when compared to the Mo–O bonding (“chemical shift”). The electrical transport properties of the samples are strongly different from SrMoO3. It was found that the conductivity of the samples decreases with increasing nitrogen content. The Seebeck coefficient values are up to three times higher than those of SrMoO3.