Preparation and Electrochromism of RF-Sputtered TiO 2 Films

Titanium oxide ( TiO 2 ) thin films were prepared by rf-sputtering in an Ar/O 2 atmosphere from a compressed powder TiO 2 target and their electrochromic (EC) phenomena were investigated. Films prepared under the sputtering pressures of 1.3, 4.0 and 6.7 Pa were confirmed by X-ray diffraction to be in amorphous state, anatase form and rutile form, respectively. Amorphous and anatase films showed cathodic EC properties. The maximum value of coloration efficiency was 14 cm 2 /C for the amorphous films in an electrolyte solution of 1N HCl. AC conductance measurements were measured from 110 Hz to 100 kHz for various oxygen contents in the sputtering atmosphere. The ac conductance gradually decreased with increasing oxygen content in the region of up to 30% and was independent of oxygen content in the region of more than 30%. In the films prepared in the sputtering atmospheres of oxygen contents of less than 30%, electronic conduction is interpreted to occur due to lack of oxygen. In the films prepared in oxygen contents of 30% and more, on the other hand, only ionic conduction is considered to exist.