CRYSTAL MODULATION OF TUNGSTEN-OXIDE GELS AND FILMS PREPARED BY THE SOL-GEL PROCESS USING 2,4-PENTANEDIONE AS AN ORGANIC LIGAND

Tungsten oxide gels and films were prepared by the sol-gel process usi ng 2,4-pentanedione (PTN) as an organic ligand. WO3 powders were obtai ned by peeling the films from the quartz glass substrates. The crystal structure of both the gels prepared with and without PTN and fired at 700 degrees C was monoclinic. WO3 powders peeled from film samples pr epared both with and without PTN showed only the monoclinic crystal st ructure, whereas the crystal phases of both types of films were cubic and a mixture of cubic and monoclinic crystals, respectively. These re sults indicate that the cubic crystals of the WO3 in the films were tr ansformed to the monoclinic crystals of the powders after the films we re peeled from the quartz glass substrates. It is concluded that the c ubic crystals in the films are transformed to stable monoclinic crysta ls by the peeling process, whereas PTN and the quartz glass substrate can control the crystal phase of WO3 films selectively to form the cub ic structure.