Ceramics-Silikáty 59 (2) 96-102 (2015)

PHYSISORPTION OF WATER ON SiO₂–TiO₂–Al₂O₃ FILMS STUDIED BY IMPEDANCE SPECTROSCOPY

The influence of film composition and surface roughness on process of physisorption of water on SiO₂–TiO₂–Al₂O₃ films prepared by sol-gel method was studied by impedance spectroscopy. The composition of prepared films, expressed by SiO₂:TiO₂:Al₂O₃ ratio, was in the range of following molar ratio: 0:0.95:0.05; 0.32:0.63:0.05; 0.475:0.475:0.05; 0.63:0.32:0.05; 0.95:0:0.05. Complex impedance spectra of thin film sensor for various relative humidities were measured in the range of 0.13 - 97.7 % and the frequency range was 1 kHz to 1 MHz. Measured dependences of complex impedance on frequency were processed by complex nonlinear least squares method. Serial connection with different counts of -(R/C)-, -(R/CPE)- and -R- equivalent circuits was used to analyse obtained spectra. The equivalent circuits were associated with physisorption of water, space charge polarization regions, and bulk or surface conductivity of the films. The dependencies presence of the relaxation processes on the value of relative humidity is used to analyse the process of water physisorption and determine composition influence, too.

Keywords: Sol-gel, Films, Physisorption of water, Impedance spectroscopy