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

In this communication, the effect of dysprosium (Dy) substitution on the structural and thermoelectric properties of LaCoO₃ in the low-temperature regime (90–325 K) have been investigated. Dy³⁺, with its smaller ionic radius and 4f electrons, induces lattice contraction, strain, phonon scattering, and modifies carrier concentration and Co³⁺ spin states, affecting both phonon and electronic transport. Polycrystalline samples La_1−xDy_xCoO₃ (x = 0, 0.1, 0.2, 0.3, and 0.4) were synthesized using solid-state reaction route. XRD showed pristine LaCoO₃ has a rhombohedral $R\overline{3}c$ structure, while Dy-doped samples (x ≥ 0.2) exhibited Dy₂O₃ secondary phase ($\mathrm{Ia}\overline{3}$). 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/mK² at 325 K. Overall, this systematic study establishes how Dy doping modifies the spin-charge-lattice interactions in LaCoO₃, highlighting its limited potential for improving thermoelectric performance in the low-temperature regime.