Enhanced electrical and thermoelectric properties of Er3⁺-doped TiO2 nanoparticles synthesized via ball milling

Abstract This study investigates the impact of erbium (Er3⁺) doping on the structural, thermoelectric, and electrical properties of titanium dioxide (TiO 2 ) nanoparticles synthesized via a straightforward ball milling approach. Pure TiO 2 and Er-doped TiO 2 (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 TiO 2 phase and the successful incorporation of Er3⁺, leading to a reduction in crystallite size (from 18.33 nm for pure TiO 2 to 14.19 nm for 3% Er-TiO 2 ) and an increase in lattice strain with higher doping concentrations. Density increased with doping, while molar volume decreased. Thermoelectric tests showed that pure TiO 2 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 TiO 2 . 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 TiO 2 for potential thermoelectric applications.