<p>This study investigates the impact of erbium (Er3⁺) doping on the structural, thermoelectric, and electrical properties of titanium dioxide (TiO₂) nanoparticles synthesized via a straightforward ball milling approach. Pure TiO₂ and Er-doped TiO₂ (1%, 2%, and 3% Er) nanocrystalline powders were prepared and characterized using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), density measurements, Seebeck coefficient analysis, and DC conductivity measurements. XRD and HRTEM results confirmed the formation of the anatase TiO₂ phase and the successful incorporation of Er3⁺, leading to a reduction in crystallite size (from 18.33 nm for pure TiO₂ to 14.19 nm for 3% Er-TiO₂) and an increase in lattice strain with higher doping concentrations. Density increased with doping, while molar volume decreased. Thermoelectric tests showed that pure TiO₂ and the sample with 1% Er-doping conducted electricity in a p-type manner, but at higher temperatures, the samples with 2% and 3% doping showed both p-type and n-type conduction. Crucially, Er3⁺ doping significantly enhanced the DC electrical conductivity and thermoelectric power (TEP) factor compared to undoped TiO₂. The conduction mechanism in the high-temperature region was identified as non-adiabatic small polaron hopping (SPH), with the improved conductivity attributed mainly to increased hopping carrier mobility. These findings highlight the effectiveness of Er3⁺ doping via ball milling in tailoring the properties of TiO₂ for potential thermoelectric applications.</p>