Abstract
OMCVD of TiO2-SnO2 mixed films using titanium isopropoxide and tetrabutyltin as starting materials was investigated. In the temperature region between 500° and 550°C crystalline films with desired composition were obtained. Pure titania films had the anatase crystal form, but the doped ones with more than 25% SnO2 exhibited the rutile form. The size of crystallites in as-deposited films depended on the film composition and was found to be smallest near Ti/Sn ratio of 1:1. When the films were annealed at 1000°C over 50h, the crystalline size increased, however, its composition dependence was the same as that in as-deposited films. From this tendency and the composition dependence of lattice constants of the annealed films, it is concluded that the phase separation takes place through the spinodal decomposition during heat treatment. The as-deposited mixed films had no photo-conductivities but had moderate dark conductivities which strongly depended on the ambient gas components. Thus they are applicable to a basic material for gas sensors.
