Neutron and X-ray powder diffraction studies of the oxynitrides SrW(O,N)(3), Ba3W2(O,N)(8) and Ba3Mo2(O,N)(8)

Oxynitrides of composition SrW(O,N)(3), Ba3W2(O,N)(8) and Ba3Mo2(O,N)(8) have been prepared by the ammonolysis of stoichiometric mixtures of oxides and carbonates. Combined Rietveld refinements of powder neutron and powder X-ray diffraction data have allowed the structure of each to be determined. SrW(O,N)(3) was found to have a cubic Perovskite structure whereas Ba3W2(O,N)(8) and Ba3Mo2(O,N)(8) have a layered hexagonal structure. In the hexagonal structures the oxygen and nitrogen atoms are distributed almost randomly over two sites in the unit cell producing 4-fold co-ordination to tungsten and molybdenum, a distorted octahedral co-ordination to one barium site and a 10-fold co-ordination to the other