Defect-mediated n-type to p-type transition and enhanced thermoelectric performance in Bi1.8−xNixSb0.2Te3 alloys

A systematic investigation pertaining to the low temperature (10–350 K) thermoelectric properties of Ni substituted Bi 1.8− x Ni x Sb 0.2 Te 3 alloys ( x = 0–0.08), it was synthesised employing solid state reaction method. X-ray diffraction studies verified the presence of phase pure rhombohedral structures. FESEM micrographs showed a morphological transition from hexagonal platelets to granular networks as the Ni content increased. Electrical transport measurements revealed a transition from n-type to p-type conduction for the sample x ≥ 0.06. This transition is attributed to the formation of acceptor defects, which increases the hole concentration as a majority charge carriers. The thermal conductivity decreased systematically from 1.7 to 1.0 Wm −1 K −1 at 350 K with substitution of Ni concentration, as a result of the increased phonon scattering due to the mass disorder and strain fields. The optimal composition ( x = 0.04) unveiled a maximum $$PF$$ and $$ZT$$ of 335 μW/mK 2 and 0.09 respectively at 350 K, $$ZT$$ has 125% increment over the pristine sample. These results validates that Ni doping effectively decouples thermal and electronic transport properties via controlled defect engineering. This controlled doping represents a viable strategy for advancing thermoelectric performance of Bi–Sb–Te system.