Orientation of tungsten trioxide thin films fabricated by sol–gel method using aqueous sols of colloidal layered tungstates |
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Authors: | Takayuki Ban Toshihiro Ito Yutaka Ohya |
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Affiliation: | 1. Department of Chemistry and Biomolecular Science, Gifu University, Yanagido 1-1, Gifu, 501-1193, Japan
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Abstract: | Oriented monoclinic WO3 thin films were fabricated by sol–gel method using aqueous sols of colloidal layered tungstates. The colloidal tungstate sols were prepared by reacting different alkylamines with layered tungstic acid H2WO4 in water. With decreasing the alkyl chain length of the alkylamines, the colloidal layered tungstate became smaller. Alkylamines with a short alkyl chain provided transparent aqueous sols. Furthermore, the WO3 thin films fabricated from the obtained aqueous sols had a high (100)-orientation. However, upon annealing H2WO4 crystals applied on a glass substrate with the tungstate layers parallel to the substrate, highly (001)-oriented WO3 layers were obtained. Since both of the A- and C-planes of WO3 have a similar structure to the layers of H2WO4, the orientation of the WO3 thin films and layers probably resulted from the topotactic structural conversion of the tungstates. Interestingly, the preferential orientation of the thin films was dependent on the presence or absence of interlayer alkylamines in the tungstates. |
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