Optimized Electronic Bands and Ultralow Lattice Thermal Conductivity in Ag and Y Codoped SnTe

Achieving High Thermoelectric Performance of Eco-Friendly SnTe-Based Materials by Selective Alloying and Defect Modulation

Recently, rock-salt lead-free chalcogenide SnTe-based thermoelectric (TE) materials have been considered an alternative to PbTe because of the nontoxic properties of Sn as compared to Pb. However, high carrier concentration that originated from intrinsic Sn vacancies and relatively high thermal conductivity of pristine SnTe lead to poor TE efficiency, which makes room for improving its TE properties. In this study, we present that the Na incorporation into the SnTe matrix is helpful for modifying the electronic band structure, optimization of carrier concentration, introducing dislocations, and kink planes; benefiting from these synergistic effects obviates the disadvantages of SnTe and makes a significant improvement in TE performance. We reveal that Na favorably impacts the structure of electronic bands by valence, conduction band engineering, leading to a nice enhancement in the Seebeck coefficient, which exhibits the highest power factor value of 37.93 μWcm^-1 K^-2 at 898 K, representing the best result for the SnTe material system. Moreover, a broader phonon spectrum is introduced by new phonon-scattering centers, scattered by dislocations and kink planes which suppressed lattice thermal conductivity to 0.57 Wm^-1 K^-1 at 898 K, which is much lower than that of pristine SnTe. Ultimately, a maximum ZT of 1.26 at 898 K is achieved in the Sn_1.03Te + 3% Na sample, which is 97% higher than that of the pristine SnTe, suggesting that SnTe-based materials are a robust candidate for TE applications specifically, an ideal alternative of lead chalcogenides for TE power generation at high temperatures.

Synergistically Optimized Electron and Phonon Transport of Polycrystalline BiCuSeO via Pb and Yb Co-Doping

Polycrystalline BiCuSeO is considered as a promising thermoelectric material due to its intrinsically low thermal conductivity and moderate Seebeck coefficient. However, its low electrical conductivity and coupled electron-phonon transport properties restrict the further improvement of the thermoelectric performance. In this work, Pb and Yb dopants are incorporated into BiCuSeO to substitute for Bi sites via ball milling and high-pressure and high-temperature sintering, leading to a synergistic optimization of the electron and phonon transport and improved thermoelectric performance. The carrier concentration exhibits an enhancement with increasing Pb&Yb co-doping contents. Meanwhile, the decreased carrier mobility is suppressed appropriately by coordinating with the interplay of Pb and Yb dopants on the electronic structure. Besides, Pb&Yb co-doping combined with high-pressure and high-temperature sintering introduces abundant grain boundaries, dislocations, and point defects to effectively decrease the lattice thermal conductivity by scattering phonons in a broad frequency range. Coupled with the synergistic optimization of the electrical and thermal properties, a maximum zT of 1.2 is achieved in Bi_0.88Pb_0.06Yb_0.06CuSeO at 850 K, which significantly outperforms the majority of oxygen-containing thermoelectric materials. Our study suggests that dual doping of bivalent ions and rare-earth elements at Bi sites is an effective strategy for improving the thermoelectric performance of BiCuSeO.

Native Atomic Defects Manipulation for Enhancing the Electronic Transport Properties of Epitaxial SnTe Films

P-type SnTe-based compounds have attracted extensive attention because of their high thermoelectric performance. Previous studies have made tremendous efforts to investigate native atomic defects in SnTe-based compounds, but there has been no direct experimental evidence so far. On the basis of MBE, STM, ARPES, DFT calculations, and transport measurements, this work directly visualizes the dominant native atomic defects and clarifies an alternative optimization mechanism of electronic transport properties via defect engineering in epitaxially grown SnTe (111) films. Our findings prove that positively charged Sn vacancies (V_Sn) and negatively charged Sn interstitials (Sn_i) are the leading native atomic defects that dominate electronic transport in SnTe, in contrast to previous studies that only considered V_Sn. Increasing the substrate temperature (T_sub) and decreasing the Te/Sn flux ratio during film growth reduces the density of V_Sn while increasing the density of Sn_i. A high T_sub results in a low hole density and high carrier mobility in SnTe films. The SnTe film grown at T_sub = 593 K and Te/Sn = 2/1 achieves its highest power factor of 1.73 mW m^-1 K^-2 at 673 K, which is attributed to the optimized hole density of 2.27 × 10²⁰ cm^-3 and the increased carrier mobility of 85.6 cm² V^-1 s^-1. Our experimental studies on the manipulation of native atomic defects can contribute to an increased understanding of the electronic transport properties of SnTe-based compounds.

Anion exchanged Cl doping achieving band sharpening and low lattice thermal conductivity for improving thermoelectric performance in SnTe

Cl doping achieves band sharpening as a potential strategy for improving the power factor in SnTe thermoelectrics.