Electrical conductivity and dielectric relaxation in non-crystalline films of tungsten trioxide

Amorphous tungsten trioxide (a-WO3) thin films were prepared by thermal evaporation technique. The electrical conductivity and dielectric properties of the prepared films have been investigated in the frequency range from 100 Hz to 100 kHz and in the temperature range 293-393 K. In spite of the absence of the dielectric loss peaks, application of the dielectric modulus formulism gives a simple method for evaluating the activation energy of the dielectric relaxation. The frequency dependence of sigma(omega) follows the Jonscher's universal dynamic law with the relation sigma(omega) = sigma(dc) + A omega(s), where s is the frequency exponent. The conductivity in the direct regime, sigma(dc), is described by the small polaron model. The electrical conductivity and dielectric properties show that Hunt's model is well adapted to a-WO3 films. (c) 2007 Elsevier B.V. All rights reserved.