Structural characterization and testing the heat gain performance of nano-sized pure and heavy metal doped SiO2–NiO xerogel for potential low-emissivity coating applications

Abstract A series of binary SiO₂–NiO xerogels was synthesized via the sol–gel technique, along with ternary xerogels in which part of the NiO content was substituted with heavy metal oxides (HMOs) such as CdO or Bi 2 O 3 .These xerogels were applied as thin coatings on glass substrates to assess their effectiveness in reducing solar heat gain. Structural characterization using FTIR and Raman spectroscopy confirmed the presence of characteristic vibrational modes associated with tetrahedral SiO 4 units, the fundamental building blocks of the silica network. The results also revealed molecular-level incorporation and interaction of NiO and heavy metal oxides (HMOs) within the silica matrix. X-ray diffraction (XRD) patterns exhibited weak intensity but discernible crystalline phases, indicating low crystallinity while providing valuable insights into phase formation. High-resolution transmission electron microscopy (HRTEM) revealed nanoscale structural features with particle sizes ranging from 1.7 to 9.1 nm, showing the coexistence of crystalline domains within an amorphous xerogel matrix. Complementary high-resolution scanning electron microscopy (HRSEM) images displayed clear crystalline structures in the thin films, confirming that nucleation and growth occurred during synthesis. Among the synthesized coatings, the ternary SiO 2 –NiO–CdO xerogel film demonstrated a significantly higher reduction in solar heat gain compared to the binary and Bi-containing samples. The data reveal the potential of Ni–Cd-based xerogel coatings as efficient low-emissivity (Low-E) materials for energy-saving window applications, particularly in environments where thermal comfort and energy efficiency are essential.