Transport reconstruction across a p-to-n polarity crossover in lone-pair-matched Bi/Sb co-doped Pb0.5Sn0.5Te

초록

Bi/Sb co-doping was introduced into p-type Pb0.5Sn0.5Te to examine how lone-pair-matched cation-site substitution reconstructs carrier transport across a p-to-n polarity crossover using Bi3+ (6s2) and Sb3+ (5s2). X-ray diffraction and X-ray photoelectron spectroscopy confirmed incorporation of Bi and Sb while preserving the host rock-salt crystal structure over the investigated composition range of x = 0 – 0.04 in Pb0.5-xBixSn0.5-xSbxTe. Hall and thermoelectric transport measurements showed that increasing x systematically drives the system from p-type to n-type conduction, with the crossover occurring between x = 0.01 and 0.02. Among the investigated compositions, x = 0.01 showed the most favorable transport balance, whereas further co-doping caused a pronounced deterioration in mobility, power factor, and thermoelectric figure of merit zT after polarity reversal. Thermal transport analysis further showed that the total thermal conductivity decreased from about 2.92 W/mK for x = 0 to about 0.95 W/mK for x = 0.04 at 300 K, mainly because of suppression of the electronic contribution, while the estimated lattice thermal conductivity displayed a non-monotonic composition dependence. Density functional theory calculations for both the pristine host and a Bi/Sb co-doped supercell revealed an intrinsic asymmetry between the valence-band-side and conduction-band-side electronic structures near the Fermi level. In the co-doped supercell, the Fermi level is displaced across the gap into the conduction band, where the projected density of states is substantial, indicating that the additional electrons occupy conduction-side states. This calculated band-edge asymmetry is consistent with the experimentally observed deterioration of the intrinsic mobility and transport quality after the system enters the n-type branch. These results suggest that Bi/Sb co-doping serves not only as a carrier-tuning route but also as a sensitive probe of transport reconstruction in this narrow-gap chalcogenide and that the host electronic structure is intrinsically more favorable for p-type than for n-type charge transport. © 2026

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