Growth, structure, dielectric and AC conduction properties of solution grown PVA films

Polyvinyl alcohol (PVA) films were deposited on pre-cleaned glass substrates using an isothermal immersion technique. Sandwich structures of the type Al-PVA-Al were formed to study the dielectric and conduction properties of PVA films. Aluminium electrodes were deposited by vacuum evaporation method. Thicknesses (d) of the dielectric films were measured by an electronic linear thickness measuring instrument (Tesatronic TTD20 model) and a gravimetric method and cross checked by a capacitance method. The dependence of the thickness of the PVA films on the immersion time, concentration and temperature of the solution had been studied. From the X-ray diffraction studies the structure of the deposited film was found to be amorphous. The dielectric properties were studied in the frequency range 1-30 kHz at various temperatures in the range 303-423 K. The capacitance, though dependent on frequency and temperature, was found to be almost invariant at room temperature for all frequencies. The dielectric constant epsilon' of the films was found to be increasing with increase in thickness of the film. The loss factor epsilon " was found to be increasing with increase in temperature up to the glass transition temperature (T-g) and decreasing above that (T-g). From AC conduction studies it was confirmed that the mechanism responsible for conduction is mostly due to ionic hopping. The films showed very high transmittance in the visible to near IR region. (C) 1999 Elsevier Science S.A. All rights reserved.