Synthesis and analysis of electrical and optical investigations of ZnO-doped sodium-titanium-silicate glasses

The development of multifunctional glass materials with tunable electrical and optical properties is critical for applications in optoelectronics, energy conversion, and smart technologies. In this study, the effect of ZnO incorporation on the electrical and optical behavior of sodium-titanium-silicate-based glasses was investigated. Glass samples with compositions of 1TiO2 - 1Al2O3 - 3CaO - 25Na2O - (70−x)SiO2: xZnO (x = 0, 5, 10, 15) were synthesized by melt-quenching technique at 1500 °C, and annealed at 450 °C. The structural modifications induced by varying ZnO content were evaluated through electrical conductivity and optical property measurements. Temperature-dependent electrical conductivity was measured between 65 and 420 K using a cryostat-integrated Keithley 6514 setup. Room temperature resistivity values showed minimal variation with ZnO addition. However, temperature-dependent electrical conductivity measurements revealed two distinct conduction regimes. At higher temperatures, conductivity exhibited classical Arrhenius behavior, while at lower temperatures, conduction followed a small polaron hopping (SPH) mechanism. Increasing ZnO content led to higher activation energies, attributed to the role of ZnO as a network former, reducing non-bridging oxygen (NBO) density and limiting Na+ ion mobility. Optical characterization was carried out using UV–VIS spectroscopy and spectroscopic ellipsometry. Transmittance spectra (300–900 nm) revealed enhanced transparency in the visible region with increasing ZnO, while (αhν)1ᐟ2 vs. hν analysis indicated a widening of the optical band gap. Urbach energy (EU) and defect-related energy (Ed) values decreased with ZnO addition, suggesting reduced localized states. Notably, a sharp absorption near 380–400 nm indicated potential ZnO cluster formation. Spectroscopic ellipsometry in the 1200–1600 nm range, modeled using the Cauchy-Urbach approach, showed good agreement between experimental and theoretical data. A consistent decrease in refractive index values was observed with increasing ZnO content.