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Cu 5 Sn 2 Se 7 is a new family member of ternary Cu-based chalcogenides that consists of abundant and environmental friendly elements. It shows a great potential for thermoelectric application, but its metal-like electronic transport behavior leads to overall low thermoelectric performance. In this work, we successfully lower the intrinsically high hole concentration of Cu 5 Sn 2 Se 7 via an aliovalent doping approach, i.e. replacing the monovalent Cu by divalent Zn. It is shown that one single parabolic band model reasonably fits the room temperature carrier concentration dependent Seebeck coefficients of Cu 5−x Zn x Sn 2 Se 7 (x = 0–1) samples with a large effective mass of 2.5 m 0, and their power factors are significantly optimized by charge carrier concentration regulation. Moreover, these materials display ultralow lattice thermal conductivity close to the theoretical minimum (0.55 Wm−1K−1) at high temperatures because of its large Grüneisen parameter of ∼2 estimated by sound velocity data. Altogether, a maximum ZT of 0.51 is achieved at 750 K for Cu 4.1 Zn 0.9 Sn 2 Se 7 , which is 325% higher over the control sample Cu 5 Sn 2 Se 7 (ZT = 0.12 @ 750 K). • The thermoelectric properties of Cu 5−x Zn x Sn 2 Se 7 were systematically investigated. • Overcome the intrinsically high hole concentration of Cu 5 Sn 2 Se 7 and enhance its TE performance by using Zn as doping agent. • The electrical transport properties of Cu 5 Sn 2 Se 7 are explored through a SPB model. • A maximum ZT of 0.51 is achieved at 750 K for Cu 4.1 Zn 0.9 Sn 2 Se 7 , which is 325% higher than that of pristine Cu 5 Sn 2 Se 7. [ABSTRACT FROM AUTHOR]

Tin sulfide (SnS), a typical IV–VI compound with low-cost, abundant-earth and eco-friendly elements, has aroused widespread attentions in the thermoelectric community due to its similar electron and phonon structures with SnSe. However, undoped SnS possesses the features of low carrier concentration and inferior band structures, which produces indecent thermoelectric performance. In this work, we successfully resolved these shortcomings of SnS through stepwise Na doping and Se alloying. Firstly, the carrier concentration of SnS was increased and optimized through Na doping, which leads to an enhancement both in electrical conductivity and Seebeck coefficients through activating multiple valance bands. Secondly, the electronic band structure of SnS was modified through Se alloying, both narrowing band gap and flatting valence band shape contribute excellent electrical transport properties, resulting in maximum power factor ∼6.0 μWcm−1K−2. After synergistically optimizing interdependent thermoelectric parameters through Na doping and Se alloying, a record high ZT of 0.70 at 873 K was obtained in polycrystalline SnS. Our work indicates that SnS is one of very promising earth-abundant thermoelectric materials for power generation in mediate-temperature range. • Power factor of p -type SnS was improved from 2.5 μWcm−1K−2 to 4.8 μWcm−1K−2 at 923 K through Na doping. • Power factor of p -type SnS was improved from 4.8 μWcm−1K−2 to 6.0 μWcm−1K−2 at 873 K through Se alloying. • ZT max of p -type SnS is distinctly enhanced from 0.25 to 0.70 at 873 K after Na doping and Se alloying. [ABSTRACT FROM AUTHOR]

Abstract In this work, we report that the high performance of SnTe could be realized by enhancing electrical transport properties (power factor) and reducing thermal conductivity through stepwisely introducing elements of Sb, In and Se. We found that Sb and In co-doping can enhance Seebeck coefficients in the broad temperature range via optimizing carrier density and introducing resonant state, respectively. Moreover, nanostructures could be formed when the Sb content beyond the solubility limit in SnTe matrix, which coupled with point defects from In and Se alloying result in a very low (lattice) thermal conductivity through the enhanced phonon scattering from defects and grain boundaries. A peak ZT ∼1.0 at 923 K can be achieved with the enhanced power factor and reduced thermal conductivity. Accordingly, the average ZT value increases from ∼0.20 for undoped SnTe to ∼ 0.60 for multiple-doped SnTe (Sn 0.823 Sb 0.17 In 0.007 Te 0.98 Se 0.02) over 300–923 K, generating a high calculated conversion efficiency ∼ 11%. Present results indicate the high performance of SnTe can be obtained through stepwisely optimizing strategy in both electrical and thermal transport properties. Highlights • A stepwisely enhancing in thermoelectric transport properties were achieved in p -type SnTe. • Power factor of p -type SnTe was enhanced from ∼3.4 μW cm−1 K−2 to ∼ 11.7 μW cm−1 K−2 at 300 K through Sb and In co-doping. • κ lat of p -type SnTe was reduced from ∼3.4 Wm−1K−1 to ∼ 1.4 Wm−1K−1 at 300 K through Sb, In co-doping, and Se alloying. • ZT ave of p -type SnTe is distinctly enhanced from ∼0.2 to ∼0.6 over 300–923 K. [ABSTRACT FROM AUTHOR]

We report n-type PbTe with a maximum ZT ∼1.2 at 673 K and an average ZT ave ∼0.84 at 300–823 K, which was achieved through a Sn and Se co-alloying approach. We find that the lattice thermal conductivity can be largely reduced through introducing Se in Te sites, and the power factor can be enhanced through introducing Sn in the Pb sites. Combining two strategies via Se and Sn co-alloying in PbTe, results show that the lattice thermal conductivity at 300 K can be reduced from ∼3.1 Wm −1 K −1 to ∼1.2 Wm −1 K −1 after alloying 15% Se, which is consistent with the Callaway model. Meanwhile, we find that both carrier concentration and mobility can be enhanced through alloying small amount of Sn, which are supported by DFT calculation with emphasis on the defect formation energies. The improvement on electrical conductivity elucidates an enhanced power factor at 300 K increasing from ∼6.4 μWcm −1 K −2 to ∼14.6 μWcm −1 K −2 . Through synergistically optimizing electrical and thermal transport properties of n-type PbTe via Sn and Se co-alloying, the ZT value is distinctly enhanced to 1.2 at 673 K, and the average ZT ave value is improved by ∼35%, from ∼0.62 in PbTe 0.997 I 0.003 to ∼0.84 in Pb 0.995 Sn 0.005 Te 0.847 Se 0.15 I 0.003 , ensuring a high maximum thermoelectric conversion efficiency ∼10.7%. [ABSTRACT FROM AUTHOR]

As an earth abundant material, PbS, has been paid extensive attention in the thermoelectric community. The high lattice thermal conductivity of PbS indicates there is room left to further improve thermoelectric performance of PbS. In this system we aimed to reduce the lattice thermal conductivity through nanostructuring grain sizes, which was processed by mechanical alloying followed by spark plasma sintering. We found that the lattice thermal conductivity can be reduced from ∼1.5 W m −1 K −1 at 723 K for PbS ingot to as low as ∼0.50 W m −1 K −1 for the PbS with nano-scale grain sizes, as a result, a ZT value of 0.80 at 723 K was achieved for 1.0% PbCl 2 doped PbS with the second phases of Bi 2 S 3 (Sb 2 S 3 , SrS, CaS). These results indicate that PbS is a robust alternative of PbTe and PbSe for medium temperature thermoelectric applications. [ABSTRACT FROM AUTHOR]

Abstract: We report on the effect of Mg doping on the thermoelectric properties of p-type BiCuSeO oxyselenide, with layer structure composed of conductive (Cu2Se2)2− layers alternately stacked with insulating (Bi2O2)2+ layers. The substitution of Bi3+ by Mg2+ leads to an enhancement of the electrical conductivity and a decrease of the thermal conductivity. Coupled to high Seebeck coefficients, ZT at 923K is increased from 0.45 for pristine BiCuSeO to 0.67 for Bi0.95Mg0.05CuSeO. However, the efficiency of Mg doping in the insulating (Bi2O2)2+ layer is low, and this doping only leads to a limited increase of the hole carriers concentration. Therefore Mg doped BiCuSeO has relatively low electrical conductivity which makes its thermoelectric figure of merit much lower than that of Ca, Sr and Ba doped BiCuSeO. [Copyright &y& Elsevier]