CRYSTAL-STRUCTURES AND OPTICAL-PROPERTIES OF TUNGSTEN-OXIDE FILMS PREPARED BY A COMPLEXING-AGENT-ASSISTED SOL-GEL PROCESS

Tungsten oxide (WO3) films were prepared by the sol-gel process, using 2,4-pentanedione (PTN) as an organic ligand. The effect of the ligand on the crystallization and crystal structure of the WO3 films was exa mined by Raman, IR and X-ray diffraction spectroscopies, and their opt ical properties were investigated in relation to the refractive index. Tungsten oxides prepared with PTN on a quartz glass substrate and a s ilicon wafer, and those prepared without PTN on a silicon wafer are am orphous when fired at 300 degrees C. The oxides crystallized when fire d at temperatures between 300 and 500 degrees C, and the amounts of cr ystalline WO3 increased when the films were fired at 700 degrees C. On ly cubic crystals of WO3 were formed selectively on the quartz glass s ubstrates when the films prepared with PTN were fired at 500 and 700 d egrees C. However, without PTN, a mixture of cubic and monoclinic crys tals was formed under the same firing conditions. The WO3 film prepare d with PTN and fired at 500 degrees C showed a lower value for the rea l part of the complex refractive index than that for the corresponding film prepared without PTN. The WO3 film prepared with PTN did not den sify immediately after being fired, resulting in a lower value for the real part of the refractive index.