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The polycrystalline SnS with a similar layered crystal structure and band structure to SnSe exhibits enormous commercial thermoelectric potential due to its lower cost and environmentally friendly characteristics. However, the wider bandgap of SnS leads to low carrier concentration and inferior electrical transport performance. The two-dimensional interlayer hinders carrier transport, leading to interesting and mysterious anisotropic thermoelectric properties. Herein, we reported the optimized electron–phonon transport in anisotropic polycrystalline SnS by Ag doping and Se alloying, realizing a high quality factor B by multiple strategies of optimizing carrier concentration, modifying band structure, and introducing various defects; further potential performance is predicted by the single parabolic band model. Specifically, Ag-doped SnS not only significantly increases the carrier concentration and weighted mobility μw in both directions but also induces multi-scale precipitates proven by the Debye–Callaway model to suppress phonon transport. Moreover, additional Se alloying optimizes the electronic band structure and increases the Seebeck coefficient, further improving μW and boosting the maximum power factor to ∼3.72 μW cm−1 K−2 at 873 K in the out-of-plane direction. Consequently, the synergistic optimization of carrier and phonon transport achieved a high B of 0.7 and a maximum zTmax of ∼0.8 at 873 K in Ag0.02Sn0.98S0.99Se0.01. Additionally, the high B predicted a high zTmax∼1.5 based on optimized carrier transport characteristics, demonstrating the potential great-performance polycrystalline SnS. This work provides a promising avenue for optimizing the zT of polycrystalline SnS by transport engineering. [ABSTRACT FROM AUTHOR]

Transition metals have excellent valence electrical properties and unique electronic state distribution and are regarded as potential materials for improving thermoelectric performance. However, the impact of transition metals on thermoelectric materials is restricted to the solid solution limit and doping efficiency, reinforcing the shortcomings in systematic research. Here, thermoelectric properties of transition metal (Ti, V, Cr, Zr, Nb, Mo)-doped PbS are compared and analyzed systematically based on the formation enthalpy. The DFT calculation indicates that the doping (except Zr) leads to the bandgap expansion and the density of states distortion near the Fermi level, while the localization property of the latter results in an invalid resonance level. The formation enthalpy dominates the carrier concentration due to the opposite trend of carrier concentration and formation enthalpy. The formation enthalpy of Zr, Ti, and Nb doping is more negative than others, leading to the more significant optimization of carrier concentration. The Moss–Burstein effect promotes the bandgap expansion, leading to weaker bipolar effects for Zr, Ti, and Nb doping. Eventually, the thermoelectric performance for Ti, Zr, and Nb doping is superior to others at high temperature. The Hume-Rothery rule of the formation enthalpy supplementation is more suitable for the doping and alloying in thermoelectricity. Thermodynamic stability analysis based on the formation enthalpy contribute the PbS-based thermoelectric devices evaluation. The present finding demonstrates the significant effect of formation enthalpy on the thermoelectric properties of PbS and provides a useful avenue for the doping modification and thermodynamic stability analysis of other thermoelectric alloy materials. [ABSTRACT FROM AUTHOR]

As a member of the emerging MXenes family, Nb2CS2 offers distinctive superconductivity, excellent electrical properties, and outstanding chemical stability, making it potentially useful for energy storage, medical imaging, and quantum computing. Herein, we systematically investigate how ultrahigh pressure affects the electrical properties of Nb2CS2. The results indicate that Nb2CS2 retains robust superconductivity with T c > 8 K up to the maximum applied pressure of 146.8 GPa. Moreover, the upper critical magnetic field H c 2 (0) of Nb2CS2 increases with pressure, and the Pauli limit is violated at pressures greater than 120 GPa. Meanwhile, H c 2 (0) increases to 19.3 T at 146.8 GPa, which is 4.8 times greater than at the initial pressure. Further analysis suggests that the significant enhancement of H c 2 (0) below 30 GPa comes from the sharp pressure-induced rise of carrier concentration as the interlayer distance decreases, and the significant increase in H c 2 (0) above 86 GPa may come from enhanced spin–orbit coupling or the possible unconventional superconducting pairing mechanisms. These results provide insights into the superconducting properties of MXene materials and offer guidelines for further research on electronic transport in Mxenes under ultrahigh pressure. [ABSTRACT FROM AUTHOR]

Breaking the thermoelectric figure of merit zT barrier of SnTe enables it to become a promising alternative to PbTe; however, the inferior and strongly coupled physicochemical properties of pristine SnTe severely restrict the efficient optimization. Herein, we doped trivalent Sb in SnTe and incorporated SnS particles to achieve high quality factor B through a two-step optimization strategy of tuning the valence band structure and intercalating heterostructural precipitates, and well predicted the potential prospects. The high solubility limit of Sb not only reduced the carrier concentration nH but also significantly optimized the valence band structure and improved the Seebeck coefficient, thereby enhancing the weight mobility μw in the all-temperature region. Furthermore, the additional SnS, which tends to exist as precipitates with different micrometer-scale sizes, enhanced low-medium-frequency phonon scattering in a wider frequency range except for point defects scattering, suppressing the lattice thermal conductivity to 0.55 W m−1 K−1. As a result of this synergistic effect, a high B-factor of ∼0.82 greater than triple pure SnTe was obtained in Sn0.91Sb0.09Te-10%SnS, with an enhanced zT of ∼1.15 at 850 K. More importantly, the high B-factor accurately predicted an excellent zT value of ∼1.65 at the optimal Fermi level, which highlights the great potential of Sn1-xSbxTe-y%SnS-based materials. This work provides an effective route for stepwise optimization of electrical and thermal performance from the B-factor perspective and has guiding significance for other thermoelectric materials. [ABSTRACT FROM AUTHOR]

As the pseudo-binary alloys between GeTe and Sb2Te3, GeSbTe-based compounds are promising thermoelectric materials. Although Ge2Sb2Te5 and GeSb2Te4 have widely been studied, the thermoelectric properties of GeSb4Te7 have not been well understood yet. In this work, we design a series of GeSb4-xBixTe7 solid solutions and systematically study the variation in the crystal structure, electrical, and thermal transport properties. Alloying Bi effectively reduces the carrier concentration and, thus, enhances the Seebeck coefficient. Meanwhile, the thermal conductivity is greatly reduced via large mass fluctuations. A maximum zT of 0.69 at 550 K and an average zT value of 0.52 between 300 and 700 K have been achieved for GeSb1.5Bi2.5Te7. These findings will promote the understanding and development of GeSbTe-based thermoelectric materials. [ABSTRACT FROM AUTHOR]

A decrease in valence band energy offset can considerably improve the thermoelectric performance of SnTe, and alloying CdTe in SnTe has been confirmed to be efficient for inducing band convergence. However, the low solubility of CdTe in SnTe severely limits the further decrease in the energy offset and the reduction of lattice thermal conductivity. Inspired by the high solubility of Sb in SnTe-based thermoelectric materials, the trivalent Sb is introduced into SnTe–CdTe alloys, aiming at manipulating the thermoelectric transport properties. Combined with the valence band model, it is demonstrated that high concentration of Sb in SnTe–CdTe enables a further optimization in valence band structures, resulting in an improvement in density-of-state effective mass, thus significantly reinforces the power factor in the whole temperature range. Meanwhile, we propose the solid solution mode of Sb in SnTe, which always generates vacancies to balance the valence state, and the introduction of vacancies explains the reduced lattice parameters and almost constant carrier concentration. Particularly, the Debye–Callaway model quantitatively compares the contribution of Sb substitutional defects and vacancy defects. As a result, an enhanced zT of ∼1.1 has been achieved for Sn0.83Cd0.05Sb0.12Te at 823 K. This work clearly shows the critical role of Sb for enhancing the thermoelectric performance of SnTe–CdTe materials. [ABSTRACT FROM AUTHOR]

AgCrSe2, which crystallizes in alternative layers of Ag+ and CrSe2− octahedral structure, has shown great potential as good thermoelectric material due to its unique ultralow lattice thermal conductivity. In this work, compound Cr2/3Te is alloyed with the matrix Ag0.97CrSe2 and the carrier concentration ranges within 1018–1020 cm−3, enabling a reliable assessment of transport properties based on single parabolic band model at room temperature. Moreover, homogeneous nanoprecipitate is observed in the matrix for high Cr2/3Te content samples, which leads to the scattering of main heat carrier of long-wavelength phonons, and thus a slight reduction of lattice thermal conductivity (∼0.3 W/m K) compared with intrinsic AgCrSe2. Combined with the optimized carrier concentration and the low lattice thermal conductivity, a figure of merit zT of 0.6 at 650 K is achieved, exceeding other reported AgCrSe2 systems, demonstrating the current Ag0.97CrSe2(Cr2/3Te)x materials as good potential thermoelectrics. [ABSTRACT FROM AUTHOR]

The rich capabilities for both electronic and phonon engineering in SnTe are highly desirable for achieving high thermoelectric performance. Alloying high-solubility MnTe (∼15%) leads to substitutional defects for reducing lattice thermal conductivity and band convergence for enhancing electronic performance, and thus, an improvement of thermoelectric performance of SnTe is realized. However, there is no evidence that the electronic and phonon transport properties are fully optimized in SnTe-15%MnTe thermoelectrics, especially for the near-room-temperature (< 573 K) thermoelectric performance, which still needs a sufficient promotion. Here, the substituted 2% Bi in SnTe-15%MnTe alloys dramatically increases the near-room-temperature zT and peak zT to ∼0.72 (at 550 K) and ∼1.3 (at 850 K), respectively. Combining the experimental evidence and the first-principles calculations, we demonstrate that the prominent enhancement of electronic performance arises from the Bi-doping-driven transport valence band alignment and the carrier concentration optimization. Furthermore, the Debye–Callaway model verifies that the reduction in lattice thermal conductivity is dominated by the Bi substitutional defects. The present findings reveal the importance of transport engineering in achieving high thermoelectric performance particularly near room temperature. [ABSTRACT FROM AUTHOR]

AgCrSe2 materials have shown the potential to be the promising thermoelectric materials due to the intrinsic ultralow lattice thermal conductivity enabled by the fluid-like motion of Ag ions in crystal structures. However, what important role the Ag point defects can play in promoting liquid-like conduction still remains a mystery. Moreover, understanding the electronic transport properties, specifically for clarifying the contribution of various impurity states, is of critical importance for improving the thermoelectric performance of AgCrSe2. Here, the thermoelectric properties of AgCrSe2 with various Ag content have been systematically investigated. It is found that the carrier concentration can be modulated in a broad range by inducing deep level impurity states, enabling a transition from degenerate semiconductor to nondegenerate one and a reliable evaluation on the thermoelectric transport properties. The single parabolic band model gives a good clarification regarding the increased electronic performance. Furthermore, the enhancement of the liquid-like effect triggered by the Ag vacancies contributes to the ultralow lattice thermal conductivity (∼0.25 W m−1 K−1). Eventually, a maximum figure of merit zT of ∼0.6 is realized in Ag0.97CrSe2 at 750 K. The present findings may shed light on the improvement of thermoelectric performance in AgCrSe2 materials. [ABSTRACT FROM AUTHOR]

Numerous endeavors have been made to advance thermoelectric SnTe for potential applications. Effective strategies focus on the manipulation of transport properties, including valence band convergence, resonate state, and defect engineering. It has been demonstrated that alloying trivalent Bi or chalcogenide SnSe alone in SnTe can trigger an inherent enhancement of thermoelectric performance. However, what the critical role in the transport valence band co-doping Bi and Se in SnTe plays is still unclear. Particularly, fully evaluating the effect of band convergence on the carrier concentration-dependent weighted mobility, which dominates the electronic performance, is primary and essential for designing excellent thermoelectric materials. Here, we report that Bi doping in SnTe–SnSe alloys can derive a distinct decrease in the energy offset between the two valence bands, thus improving the density-of-state effective mass by only slightly deteriorating the mobility. The well-established theoretical model reveals that the Bi-doping-induced band convergence and the optimized carrier concentration actually enhance the weighted mobility, contributing to the improvement of electronic performance. Moreover, the Debye–Callaway model demonstrates the origin of the reduced lattice thermal conductivity. The present results confirm the potential of transport engineering in promoting thermoelectric performance. [ABSTRACT FROM AUTHOR]

The effective electron mobility in long-channel silicon-on-insulator junctionless multigate metal-oxide-semiconductor transistors is experimentally studied. It is found that the mobility in heavily doped narrow nanowire (NW) devices at low to moderately high carrier densities significantly exceeds that in wide (planar) devices with the same silicon thickness and doping and, in a certain range of carrier densities, it exceeds the mobility in bulk silicon with the same doping concentration. This effect increases when decreasing the NW width. The possible origins of this effect are discussed. These results are extremely encouraging for the development of junctionless NW transistors. [ABSTRACT FROM AUTHOR]