Multifunctional Nb–Er Co-Doped TiO₂: A Structure–Property–Function Correlation Study for Energy and Educational Applications

Abstract

Titanium dioxide (TiO₂) is widely used in energy and dielectric applications; however, its wide bandgap and rapid charge recombination limit practical performance. In this study, (Nb₀.₅Er₀.₅)xTi₁₋xO₂ (x = 0.01–0.10) was synthesised via a solid-state route to investigate the effect of Nb–Er co-doping on structure–property relationships. X-ray diffraction confirms the stabilisation of the rutile phase with dopant-induced lattice distortion and crystallite refinement. Scanning electron microscopy reveals a transition from uniform grains to agglomerated structures with increasing dopant concentration. Dielectric analysis shows strong frequency dispersion governed by Maxwell–Wagner interfacial polarisation, while impedance and modulus studies indicate non-Debye relaxation behavior. The AC conductivity follows Jonscher’s power law, confirming a hopping conduction mechanism mediated by defect states and oxygen vacancies. An optimal composition (x ≈ 0.04–0.06) exhibits enhanced dielectric constant, reduced loss and improved conductivity due to synergistic interactions between Nb donor states and Er-induced defect levels (Chen et al., 2011, Grätzel, 2001). These findings highlight the potential of Nb–Er co-doped TiO₂ for low-power solar energy systems and multifunctional applications, including compact educational devices demonstrating real-time energy conversion.