Effects of ultraviolet irradiation and corona discharge on the crystallization from NiO/SiO₂ mixed gels

Fine particles and thin films of NiO/SiO₂ mixed gels, prepared from a bidentate alkoxide, were irradiated by a XeCl excimer laser or by a corona discharge. A part of NiO was initially dissolved in SiO₂, and was segregated and crystallized on heating at 10 K min^-1 to 800°C in air. Subsequently, amorphous SiO₂ crystallized into cristobalite at 900°C. Based on the change in the interplanar spacing of cristobalite, ultraviolet irradiation or discharge promoted the segragation of NiO. Transmission electron micrographs of substrateless gel thin films revealed that corona discharge treatment brought about the formation of uniform NiO particles as small as 5 nm.