The Chloroalkoxide Route to Transition Metal Oxides. Synthesis of V2O5 Thin Films and Powders from a Vanadium Chloromethoxide

详细信息    查看全文

• 作者：Mauro Epifani ; Teresa Andreu ; Carlos R. Magana ; Jordi Arbiol ; Pietro Siciliano ; Massimiliano D’ ; Arienzo ; Roberto Scotti ; Franca Morazzoni ; Joan R. Morante
• 刊名：Chemistry of Materials
• 出版年：2009
• 出版时间：April 28, 2009
• 年：2009
• 卷：21
• 期：8
• 页码：1618-1626
• 全文大小：283K
• 年卷期：v.21,no.8(April 28, 2009)
• ISSN：1520-5002

文摘

Vanadium chloromethoxide was prepared by the methanolysis of VCl₄. The addition of water with a H₂O:vanadium molar ratio ranging between 0 and 16 changed the solution color from green to deep blue at a rate increasing with water concentration. UV−vis, Fourier transform infrared, Raman, and electron paramagnetic resonance spectroscopy investigations showed that VCl₄ precursor is initially methanolyzed to (VO)Cl_x(OCH₃)_y (x + y = 4) monomers. Upon water addition, methoxo ligands undergo hydrolysis. The presence of chlorine ligands and of the vanadyl group explains the long-term stability of the solutions. V₂O₅ thin films and powders were prepared, respectively, by spin-coating onto silicon substrates and drying of the solutions, followed by heat-treatments at temperatures up to 500 °C. Films and powder precursors were characterized by X-ray diffraction, FTIR, Raman, UV−vis, and EPR spectroscopy, transmission electron microscopy, and thermal analyses. The structural evolution begins by condensation of the initial monomers to form amorphous structures with poor extension of the three-dimensional network. Heat-treatment at higher temperatures induces further condensation and the elimination of the chlorine ligands, which leave an oxygen-defective structure and cause the initial formation of substoichiometric V₃O₇ phase. When the samples were annealed at T ≥ 400 °C, only the V₂O₅ phase was found. V₂O₅ powders annealed at 500 °C were used in chemoresistive gas sensing devices and were able to detect reducing gases such as ammonia and ethanol over a broad range of concentrations by stable and reliable signal.