Studies on the Role of <scp> Bi ₂ O ₃ NPs </scp> in Imparting Unique Optical, Dielectric, and Conductivity Properties to Nanocomposites for Energy Storage Devices

ABSTRACT In this study, flexible and transparent polyvinyl pyrrolidone/chitosan (PVP/Cs)–Bi 2 O 3 nanocomposite films were successfully fabricated using a solution casting technique with varying Bi 2 O 3 nanoparticle loadings (1–2.5 wt.%). X‐ray diffraction (XRD) showed a gradual decrease in crystallinity with increasing Bi 2 O 3 content, reflecting strong polymer–filler interactions and an increased amorphous nature. Additionally, the crystallinity index ( X c %) decreased from 36.42% to 19.71% as Bi 2 O 3 content increased, demonstrating the effect of Bi 2 O 3 nanoparticles on the polymer matrix structure. Fourier‐transform infrared (FTIR) spectra confirmed complexation between Bi 3+ ions and functional groups (CO, OH, and NH 2 ) of the host polymers. The optical properties of PVP/Cs–Bi 2 O 3 nanocomposites were investigated, revealing a decrease in the direct and indirect band gaps ( E gd and E gi ) from 4.89 and 3.90 eV for pure PVP/Cs to 2.41 and 1.74 eV for the 2.5% Bi 2 O 3 sample, respectively. The Urbach energy increased from 0.254 ± 0.002 to 0.331 ± 0.003 eV, indicating enhanced disorder with Bi 2 O 3 incorporation. Thermogravimetric analysis (TGA) demonstrated improved thermal stability due to the barrier effect and strong interfacial bonding of Bi 2 O 3 nanoparticles. Dielectric measurements showed that the dielectric constant and AC conductivity increased notably with filler content, attributed to enhanced interfacial polarization and charge carrier mobility. The PVP/Cs–Bi 2 O 3 nanocomposites exhibited high dielectric constant, low loss, and good optical transparency, making them promising candidates for energy storage, optical coatings, and flexible electronic devices.