Structural, electrical, and nonlinear optical performance of PVAL embedded with Li⁺-ions for multifunctional devices

In this paper, pure and 0.04%, 0.19%, 0.4%, 1.9%, and 4% LiNO₃-doped PVAL (polyvinyl alcohol) electrolyte were fabricated in the form of solid films by the casting process. The influence of Li⁺-ions on PVAL was identified by some characterization tools such as X-ray diffraction, FT-IR (Fourier transform infrared), scanning electron microscope (SEM), thermal gravimetric analysis (TGA), UV-visible-NIR spectroscopy, dielectric, and conductivity measurements. X-ray diffraction studies indicate that the semicrystalline of PVAL and the calculated crystallize size from Gaussian fitting were decreased with Li⁺-ions concentration. FT-IR results indicate that there is strong interaction among doping ions and the matrix. The surface morphology of the electrolyte films was studied via SEM. The optical studies demonstrate that the transmittance of films decreased with the rising of Li⁺-ions. Urbach's energy and bandgap are also reduced with adding more ions. Different empirical equations were used to study the relation between the energy gap and the refractive index. The index of refraction of the films has average values in 2.024 to 2.078 range. Li⁺-ion concentrations critically influenced the factors of nonlinearity. The calculated values of nonlinear optical susceptibility χ⁽³⁾ and refractive index n₂ were increased from 8.6 × 10⁻¹³ esu and 1.55 × 10⁻¹¹ to 20.56 × 10⁻¹⁰ esu and 2.05 × 10⁻¹¹, respectively. The dielectric constant and loss measurements of the PVAL embedded with 4% of LiNO₃ (SPL-5) were decreased exponentially with increasing the incident frequency. The AC electrical conductivity (σ_AC) and nonlinear I-V curves are enhanced by increasing the Li⁺-ion contents. The electrical current was increased with small resistivity for SPL-5 film. The studied films have an inimitable result in various fields, such as nonlinear optical and varistor devices.