Impact of Annealing Temperature on Structural, Optical, and Dielectric Properties of SnO₂ Nanostructures Synthesized via Sol-Gel Methods

This study explores the structural, morphological, optical, and dielectric properties of tin dioxide (SnO₂) nanostructures synthesized using a modified sol-gel method and thermally treated at 300°C, 400°C, and 500°C. X-ray diffraction (XRD) analysis, followed by Rietveld refinement, confirms a well-crystallized tetragonal rutile phase with improved crystallinity at higher annealing temperatures. Crystallite size, estimated using Scherrer’s formula and the Williamson-Hall method, increases with temperature, indicating reduced strain and enhanced crystal quality. High-resolution TEM images corroborate these findings, revealing well-defined lattice fringes consistent with the rutile SnO₂ phase. Morphological analyses using TEM and SEM reveal a temperature-dependent increase in particle size and agglomeration, impacting the surface area and optical characteristics of the nanostructures. UV-Vis absorption spectra show a notable shift in optical band gap energy, increasing from 3.36 eV at 300°C to 3.88 eV at 500°C, attributed to improved crystallinity and reduced defect states. Dielectric measurements exhibit a strong dependence on frequency and temperature, with a high dielectric constant observed at low frequencies that diminishes with increasing frequency due to interfacial polarization. Nyquist plots show Debye-type relaxation, indicating thermally activated conduction, while frequency-dependent ac conductivity follows Jonscher’s law, attributed to correlated barrier hopping. These findings underscore the significant role of annealing temperature in influencing the structural, optical, and dielectric properties of SnO₂ nanostructures, offering valuable insights for optimizing these materials for applications in optoelectronics, sensors, and high-frequency devices.