Zinc oxide (ZnO) continues to attract considerable attention due to its structural versatility and tunable properties at the nanoscale. Modification of ZnO through metal-oxide incorporation provides an effective strategy to control crystallinity, defect density, and microstructural evolution. In the present work, ZnO, calcium oxide (CaO)-ZnO, and bismuth(III) oxide (Bi₂O₃)-ZnO nanocomposites were synthesized via a simple sol-gel route using zinc sulphate (ZnSO₄), calcium nitrate (Ca(NO₃)₂), and bismuth sulphate (Bi₂(SO₄)₃) precursors, followed by calcination at 400 °C. Structural and morphological characteristics were systematically investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FTIR). XRD analysis confirmed the formation of crystalline wurtzite ZnO in all samples, with additional diffraction features corresponding to CaO and Bi₂O₃ in the respective composites. Incorporation of CaO resulted in reduced crystallite size and increased lattice disorder, indicating effective grain-growth suppression, whereas Bi₂O₃ incorporation promoted crystallite coarsening and enhanced crystallinity. SEM observations revealed anisotropic Bi₂O₃ microstructures embedded within the ZnO matrix, while CaO-ZnO samples exhibited densely agglomerated assemblies of nanoscale primary particles. FTIR spectra further verified the presence of characteristic metal-oxygen vibrational modes and surface-associated functional groups, supporting the structural conclusions drawn from XRD. The results demonstrate that dopant chemistry plays a decisive role in governing the nanoscale structural evolution of ZnO under identical synthesis conditions. This study establishes a clear structure-composition relationship in ZnO-based oxide nanocomposites and provides a reliable framework for further investigations aimed at controlled microstructural tailoring.

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