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.