Electrical and optical properties of pure and silver nitrate-doped polyvinyl alcohol films

doi:10.1016/S0167-577X(02)00434-2

Materials Letters

Volume 56, Issue 3, October 2002, Pages 167-174

https://doi.org/10.1016/S0167-577X(02)00434-2 Get rights and content

Abstract

The electrical conductivity, current–voltage (I–V) characteristics and optical absorption of pure and AgNO₃-doped polyvinyl alcohol (PVA) films have been studied under different conditions. The electrical conductivity increased with increasing dopant concentration up to 0.5 wt.% of the dopant and then showed a decrease beyond this concentration. The increase in conductivity for dopant concentration up to 0.5 wt.% is attributed to formation of charge transfer complexes while the decrease for concentrations above 0.5 wt.% may be due to segregation. The variation of electrical conductivity with temperature showed two regions of activation with activation energies 0.8 and 0.3 eV for undoped films and 1.3 and 0.3 eV for doped films. I–V characteristics indicated that Schottky emission is the dominant charge transport mechanism in both undoped and AgNO₃-doped films. Optical absorption studies in the wavelength range 190–600 nm showed additional peaks in the wavelength region 391–417 nm for differently doped films, in addition to the peak at 273 nm for undoped PVA. The optical energy gaps and band edge values shifted to lower energies on doping up to a dopant concentration of 0.5 wt.% but showed an increasing tendency for further increase in dopant concentration.

Introduction

In recent years, studies on the electrical and optical properties of polymers have attracted much attention in view of their application in electronic and optical devices. Electrical conduction in polymers has been studied aiming to understand the nature of the charge transport prevalent in these materials while the optical properties are aimed at achieving better reflection, antireflection, interference and polarization properties. The electrical and optical properties of polymers can be suitably modified by the addition of dopants depending on their reactivity with the host matrix. Although some work has been reported on the charge carrier transport and optical properties of doped polymers [1], [2], [3], [4], [5], [6], very little work is available on doped polyvinyl alcohol (PVA) films [7]. Polyvinyl alcohol is a potential material having a very high dielectric strength (>1000 kV/mm), good charge storage capacity and dopant-dependent electrical and optical properties. Since Ag+ is a fast conducting ion in a number of crystalline and amorphous materials, its incorporation within a polymeric system may be expected to enhance its electrical and optical performance. This paper presents the results of such investigations on the electrical and optical properties of silver nitrate-doped PVA films.

Section snippets

Experimental

Pure (undoped) and AgNO₃-doped PVA films were grown by the solution growth technique from a solution of PVA dissolved in triple distilled water with a concentration of 10% by weight of the solute. Both the polymer and dopant completely dissolved in the solvent exhibiting high solubility. The doping (to 0.25, 0.5, 0.75 and 1 wt.%) was done by mixing a desired amount of pure AgNO₃ into the PVA solution. The solution was thoroughly stirred to obtain a homogeneous mixture before the films were

Electrical conductivity

Fig. 1 shows a typical logI vs. 1000/T plot for undoped PVA for different bias field strengths. While the conductivity behaviour was independent of the applied field strength within experimental error, its temperature dependence exhibited two clear regions of activation. The conductivity increased with increase in temperature but the rate of increase was different in different temperature regions.

From the slopes of these plots, the activation energies were calculated using the Arrhenius

Conclusions

These studies indicate that PVA can be effectively doped with AgNO₃ to enhance its electrical conductivity and alter its conduction behaviour. maximum conductivity has been obtained for a dopant concentration of 0.5 wt.% of AgNO₃. This enhancement has been explained on the basis of charge transfer complex formation. Increase of dopant concentration beyond 0.5 wt. % resulted in a decrease in conductivity owing perhaps to the segregation effect. In undoped films, the charge carriers are electrons

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Electrical and optical properties of pure and silver nitrate-doped polyvinyl alcohol films

Abstract

Introduction

Section snippets

Experimental

Electrical conductivity

Conclusions

Synth. Met.

Solid State Commun.

Thin Solid Films

Thin Solid Films

J. Non-Cryst. Solids

Thin Solid Films

Phys. Rev. B: Condens. Matter

J. Phys. Soc. Jpn.

J. Mater. Sci. Lett.