Abstract
This work presents a reproducible and low-cost approach for preparing ZnAl₂O₄:SnO₂ composite thin films on glass substrates using a sol–gel dip-coating technique followed by a two-step annealing process. The films were synthesized from a Zn–Al–oxalate sol (Zn:Al = 1:2) with SnO₂ nanoparticles incorporated at 3 and 6 wt%. Deposition was carried out at a withdrawal rate of 60 mm•min⁻¹ using two coating cycles, each separated by a soft-bake at 150 °C for 10 min. The thermal consolidation involved sequential heating at 300 °C for 15 min and 480 °C for 30 min in air. Structural, chemical, and morphological properties were examined using FTIR, XRD, and AFM analyses. FTIR spectra confirmed the spinel ZnAl₂O₄ band near 655 cm⁻¹, while XRD patterns revealed a well-defined cubic spinel phase without secondary peaks. AFM images showed uniform grains and controlled roughness depending on SnO₂ concentration. Optical analysis indicated a slight redshift of the absorption edge with SnO₂ addition, and the electrical characterization showed decreased resistance and increased capacitance in the doped films. The obtained results confirm that combining ZnAl₂O₄ with SnO₂ effectively tailors both structural and functional characteristics of spinel-based thin films using a simple, entirely vacuum-free process.