Role of dysprosium in modulating low-temperature thermoelectric performance of LaCoO3 system

• La 1- x Dy x CoO 3 ( x = 0-0.4) synthesized via optimized solid-state reaction. • Structural and thermoelectric properties studied with Dy substitution. • No structural phase transition observed upon Dy incoporation. • Improved power factor; charge transport via SPH and VRH mechanisms. In this communication, the effect of dysprosium (Dy) substitution on the structural and thermoelectric properties of LaCoO 3 in the low-temperature regime (90–325 K) have been investigated. Dy 3+ , with its smaller ionic radius and 4 f electrons, induces lattice contraction, strain, phonon scattering, and modifies carrier concentration and Co 3+ spin states, affecting both phonon and electronic transport. Polycrystalline samples La 1− x Dy x CoO 3 ( x = 0, 0.1, 0.2, 0.3, and 0.4) were synthesized using solid-state reaction route. XRD showed pristine LaCoO 3 has a rhombohedral R 3 ¯ c structure, while Dy-doped samples ( x ≥ 0.2) exhibited Dy 2 O 3 secondary phase ( Ia 3 ¯ ). SEM revealed distinct grains and well-defined boundaries affecting transport properties. Electrical resistivity decreased with temperature, showing semiconducting behavior, and was described using variable range and small polaron hopping models. Dy doping increased resistivity and thermopower, reducing the power factor, with higher activation energy and carrier concentration contributing to rise in the electrical resistivity. The pristine sample had a maximum power factor of 25 μW/mK 2 at 325 K. Overall, this systematic study establishes how Dy doping modifies the spin-charge-lattice interactions in LaCoO 3 , highlighting its limited potential for improving thermoelectric performance in the low-temperature regime.