Abstract

Interstitial vanadium–chromium and chromium–molybdenum oxynitrides in the solid solution series V_1 − zCr_z(O_xN_y) and Cr_1 − zMo_z(O_xN_y) (z = 0.0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) have been obtained by direct ammonolysis of precursors resulting from the freeze-drying of aqueous solutions of the appropriate metal salts. A study of the influence of the preparative variables on the outcomes of this procedure is presented. Compounds in the V_1 − zCr_z(O_xN_y) series are prepared as single phases by nitridation at 1073 K, followed by fast cooling of the samples. Compounds in the Cr_1 − zMo_z(O_xN_y) series are prepared as nearly single phases by nitridation at different temperatures, optimized for each composition, followed by fast cooling of the samples. As for the VN, CrN and Mo₂N binary nitrides, all the V_1 − zCr_z(O_xN_y) and Cr_1 − zMo_z(O_xN_y) compounds in these series have the rock salt crystal structure, in which the metal atoms are in a fcc arrangement, with non-metal atoms occupying octahedral interstitial positions. The materials have been characterized by X-ray powder diffraction, elemental analysis, scanning electron microscopy and thermogravimetry under oxygen flow. V_1 − zCr_z(O_xN_y) and Cr_1 − zMo_z(O_xN_y) grains are aggregates of nanometric spherical particles with diameters typically around 20 nm. Surface oxidation must account to a large extent for the oxygen content of these compounds.