Study of electrical and optical properties of polyvinyl alcohol thin films doped with rare earth metal salts

Abstract

The present thesis deals with the preparation, characterization and investigation of some physical properties of polyvinyl alcohol (PVA) thin films doped with rare earth metal salts. Cast technique was used to prepare thin films of pure and EuC13 or TbCh doped PVA with dopant concentrations of5, 10, 15,20and25wt%.

Studies were carried out using X-ray diffraction, IR spectroscopy, UV­ visible spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dielectric constant, dielectric loss tangent, ac electrical conductivity and de electrical conductivity. A correlation between the investigated properties was discussed.

Preliminary X-ray structure analysis of the prepared samples indicated the formation of two conventional amorphous and crystalline phases. X-ray diffraction patterns of all composite samples under investigation proved the miscibility of EuCh or TbC13 additives in PVA matrix. The degree of crystallinity was found to depend on dopant type and concentration.

Infrared spectra of the parent components and their composites were subjected to a comparative study. The calculated index of crystallinity was found to be sensitive to both sample composition and dopant type. The obtained data are consistent with that of X-ray diffraction.

The UV-visible spectra revealed that pure EuC13 and TbCh compounds are highly absorptive than pure PVA. A shoulder-like band has been developed in the absorption spectra of the investigated composites at about 350 nm, giving further evidence for complex formation. A new band has been developed at about 220nm in the spectra of PVA-TbCh composite samples. This band is sensitive to dopant content.