Synthese en milieu hydrothermal et caractérisation de l'oxyhydroxyde de vanadium V3+OOH et d'une nouvelle variété allotropique du dioxyde VO2

Vanadium oxyhydroxide containing mostly trivalent vanadium was synthesized under hydrothermal conditions at 200°C and 2 k bar by hydrolysis of NaVO₃ previously reduced under hydrogen. The structure of VOOH is of diaspore type, isotypic with A1OOH. Oxidation of VOOH at 80°C in air gives in a few days a new metastable phase of vanadium dioxide VO₂; the structure of this new phase is also of the diaspore type, the transformation VOOH → VO₂ being topotactic. Characterization of these phases was done by X-ray diffraction, thermogravimetry, and magnetic, and electrical measurements. Both phases show semiconductor behavior and no electronic transition is observed in VO₂ (diaspore) up to 200°C.