title: Anion order in perovskite oxynitrides.
abstract: Transition-metal oxynitrides with perovskite-type structures are an emerging class of materials with optical, photocatalytic, dielectric and magnetoresistive properties that may be sensitive to oxide-nitride order, but the anion-ordering principles were unclear. Here we report an investigation of the representative compounds SrMO(2)N (M = Nb, Ta) using neutron and electron diffraction. This revealed a robust 1O/2(O(0.5)N(0.5)) partial anion order (up to at least 750 °C in the apparently cubic high-temperature phases) that directs the rotations of MO(4)N(2) octahedra in the room-temperature superstructure. The anion distribution is consistent with local cis-ordering of the two nitrides in each octahedron driven by covalency, which results in disordered zigzag M-N chains in planes within the perovskite lattice. Local structures for the full range of oxynitride perovskites are predicted and a future challenge is to tune properties by controlling the order and dimensionality of the anion chains and networks.
authors.affiliation: Centre for Science at Extreme Conditions and School of Chemistry, University of Edinburgh, King's Buildings, Mayfield Road, Edinburgh, EH9 3JZ, UK.
authors.forename: Minghui
authors.initials: M
authors.lastname: Yang
authors.forename: Judith
authors.initials: J
authors.lastname: Oró-Solé
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Rodgers
authors.forename: Ana Belén
authors.initials: AB
authors.lastname: Jorge
authors.forename: Amparo
authors.initials: A
authors.lastname: Fuertes
authors.forename: J Paul
authors.initials: JP
authors.lastname: Attfield
mesh_terms: D000838:Anions / Q000737:chemistry*; D017610:Calcium Compounds / Q000737:chemistry*; D008968:Molecular Conformation; D009584:Nitrogen / Q000737:chemistry; D010087:Oxides / Q000737:chemistry*; D014025:Titanium / Q000737:chemistry*
chemical_list: D000838:Anions; D017610:Calcium Compounds; D010087:Oxides; C059910:perovskite; D014025:Titanium; D009584:Nitrogen