Determination of stoichiometry from polycrystalline powders of transition metals lamellar dichalcogenides: MoSe2, WSe2, obtained by synthesis in laboratory

Polycrystalline molybdenum and tungsten (MoSe2, WSe2) diselenides were synthesized at 1323 K for 168 hours in silica tubes sealed secondary vacuum. They were haracterized by diffraction with X-Ray diffraction (XRD), Scanning Electron Microscopy (SEM) and gravimetric analysis show that they are homogeneous and well crystallized. Electrochemical and chemical dosages were used to determine their stoichiometry. The results have shown that stoichiometry is reached only when using B type powders and a difference in layer piling according to the mode of synthesis; this explains why A type powders differ from B type powders due to the piling of 2H: 3R layers.Keywords: Polycrystalline powders, MoSe2, WSe2, SEM, X-Ray diffraction, gravimetry and electrochemical