Phase formation, structural and microstructural characterization of novel oxynitride-perovskites synthesized by thermal ammonolysis of (Ca,Ba)MoO4 and (Ca,Ba)MoO3

Reactions of AMoO(4) and AMoO(3) (A = Ca2+, Ba2+) with ammonia were investigated at 873 K<1123 K with the particular intention to synthesize novel oxynitride-perovskites of the general composition AMo(O,N)(3) and to study their crystal structure. CaMo(O,N)(3) and BaMo(O,N)(3) were prepared by thermal ammonolysis of the Corresponding CaMoO3 and BaMoO3 precursors at T = 898 and 998 K, respectively. The structural parameters of the oxynitrides were obtained from Rietveld refinements of X-ray and neutron powder diffraction data. CaMo(O,N)(3) crystallizes in the GdFeO3 distorted perovskite structure with orthorhombic space group Pbnm and a = 5.5029(1)angstrom, b = 5.5546(1)angstrom, c = 7.8248(1)angstrom as determined by X-ray powder diffraction. Its O/N content refined from the neutron diffraction data corresponds to the composition CaMoO1.7(1)N-1.3(1). BaMo(O,N)(3) crystallizes in the cubic perovskite structure with space group Pm (3) over barm and a = 4.0657(1)angstrom as determined by X-ray powder diffraction. Transmission electron microscopy reveals a complex microstructure for both CaMoO3 and CaMoO1.7(1)N1.3(1) represented by twin domains of different orientation. (C) 2008 Elsevier Inc. All rights reserved.