The structures of three indium and one scandium complex layered oxide halides have been determined from time-of-flight powder neutron diffraction data. The indium phases Ba,InO,F, Ba,InO,Cl and Ba,InO,Br all crystallize in the space group P4/nrnm and exhibit complete oxide halide segregation, producing alternating sections of halide [ BaF] and oxide [ BaO] ions separating infinite InO, layers. However, Ba,ScO,F shows only partial oxide/fluoride ordering with the fluoride ions occupying the two apical sites on scandium equally with oxide ions, in the space group I4/mrnm. 19F MAS NMR data have been collected from Ba,InO,F and Ba,Sc03F, and confirm the structural analysis in terms of a single type of fluoride ion site in each material.The structural chemistry of complex oxide halides has become the subject of renewed interest following the recent reports of high-temperature superconductivity in various layered oxide halide cuprates. There appear to be at least three routes to these p-type oxide halide superconductors: interstitial halogen doping, cation substitution and anion substitution. Interstitial fluorine doping of Sr,CuO, affords the 46 K superconductor Sr,CuO,F,+,,' in which the fluoride ions occupy solely the apical sites about the copper, giving effective CuO, square planes and an interstitial site in the new SrF rocksalt layer.
