Freeze-dried precursor-based synthesis of new vanadium-molybdenum oxynitrides

Interstitial vanadium molybdenum oxynitrides in the solid solution series V 1 - zMoz(OxNy) (z = 0.0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) have been obtained b y direct ammonolysis of precursors resulting from freeze-drying of aqueous solutions of the appropriate metal salts. A study of the influence of the p reparative variables on the outcomes of this procedure is presented. Compou nds in this series are prepared as single phases by nitridation at 1038 K, followed by fast cooling of the samples. As for the VN and Mo2N individual nitrides, all the V1 - zMoz(OxNy) compounds in this series have the rocksal t crystal structure, in which the metal atoms are in a fcc arrangement, wit h N and O atoms occupying octahedral interstitial positions. Cell parameter s increase regularly with z, as can be expected taking into account the siz es of V and Mo atoms. The materials have been characterized by X-ray powder diffraction, elemental analysis, scanning electron microscopy and thermogr avimetry under oxygen flow. V1 - zMoz(OxNy) grains are aggregates of nanome tric spherical particles with typical diameters of ca. 20 nm. Their stabili ty in oxygen atmosphere is low but increases with the Mo content.