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Abstract: A series of LaFeAsO1−x F x (x =0–0.225) oxyarsenides have been synthesized by a solid-state reaction method in order to optimize electrical transport properties through appropriate F doping. Both electrical resistivity and Seebeck coefficient of undoped LaFeAsO show an anomaly at about 150K, which is related to a structural phase and/or spin-density-wave (SDW) transition. Seebeck coefficient seems to be determined by two competitive factors: it is enhanced by suppressing the structural phase and/or SDW transition, and reduced by increasing carrier concentration. Seebeck coefficient is significantly enhanced just after suppressing the anomaly, and the maximum Seebeck coefficient reached −142μV/K for the sample with F doping x =0.075 from −58μV/K for undoped LaFeAsO, and then decreased with further increasing carrier concentration through F doping. Meanwhile, the electrical resistivity is decreased with increasing F doping, resulting in a maximum power factor value of 1.2mW/mK2 at 80K for polycrystalline LaFeAsO0.85F0.15 sample, this value is the same order as that of the best low temperature thermoelectric Bi88Sb12 compounds, and could be significantly higher in single crystals. [ABSTRACT FROM AUTHOR]

Abstract: Highly dense n-type Bi2Te3 dispersed with x vol% nano-SiC particles (x =0, 0.1, 0.5, 1.0) thermoelectric materials were fabricated by mechanical alloying (MA) and spark plasma sintering (SPS) method. The effects of nano-SiC addition on the thermoelectric and mechanical properties were studied. Compared with Bi2Te3 matrix, Bi2Te3 materials dispersed with nano-SiC show increased Seebeck coefficient, decreased electrical conductivity, and reduced thermal conductivity as well in the measured temperature range of 323–523K. The maximum dimensionless figure of merit (ZT max) was improved from 0.99 for Bi2Te3 sample to 1.04 for 0.1vol% SiC dispersed Bi2Te3 sample at 423K. The Vickers hardness increased linearly from 0.62 to 0.79GPa as 1.0vol% SiC was added. The highest fracture toughness of 1.34MPam1/2 was obtained for 0.1vol% SiC addition, and the highest Young''s modulus of 42.7GPa was obtained for 0.5vol% SiC added sample. [Copyright &y& Elsevier]

Highly efficient thermoelectric materials always have low thermal conductivities. Their phonon spectrum information is essential for understanding the procedure of thermal transport on thermoelectrics. Recently, palladium sulfide was found to be a potential thermoelectric material. However, the high thermal conductivity limits its thermoelectric performance and technological applications. Here, the phonon dispersion and phonon density of state in PdS are presented by using the first-principles theory. The phonon modes are assigned and compared with experiments. The evolution of optical modes with pressure is studied by using Raman spectroscopy. The low-energy and high-energy phonon bands are related to the vibrations of the heavy atom and the light atom, respectively. By combining Raman scattering and X-ray diffraction measurements, we obtain the mode-Grüneisen parameters for the detected phonon modes. The small mode-Grüneisen parameters indicate a weak anharmonicity in this material. This offers an explanation for its high thermal conductivity. The evolution of linewidths with pressure accounts for the decrease of the thermal conductivity upon compression. • The phonon dispersion and phonon density of state of PdS are given in terms of first-principles theory. • The observed optical phonon modes in Raman spectra have been assigned through theoretical calculations. • The structural evolution of PdS with pressure is given from high-pressure X-ray diffraction measurements. • The mode-Grüneisen parameters of the phonon modes of PdS are obtained from experiments. [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]

Te-free PbS has been regarded as a promising alternative candidate for PbTe thermoelectric materials due to its advances of low-cost, earth-abundant. In this work, we report an enhanced thermoelectric performance in n -type PbS system arising from synergistically optimized carrier and phonon transport properties. The electrical transport properties are optimized by tuning carrier concentrations via Sb doping, resulting in a maximum power factor of ∼16.7 μWcm −1 K −2  at 623 K, which is approximately tenfold higher than that of undoped PbS (∼1.8 μWcm −1 K −2 ). PbSe and PbTe co-alloying in PbS was carried out to reduce lattice thermal conductivity through introducing point defects scattering and second phase, resulting in a minimum lattice thermal conductivity ∼0.71 Wm −1 K −1  at 923 K. Combined the enhanced power factor with suppressed thermal conductivity, a maximum ZT value ∼1.0 was obtained in n -type (PbS) 0.53 (PbSe) 0.25 (PbTe) 0.2 Sb 0.02 at 923 K. [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]

BiSbSe 3 is a promising medium-temperature thermoelectric material on account of its intrinsically low thermal conductivity. To further enhance the thermoelectric performance in n -type BiSbSe 3 , we conduct Br doping at Se sites to optimize its carrier concentration and electrical conductivity, finally a maximum ZT of ∼0.8 in nanostructured BiSb(Se 0.94 Br 0.06) 3 is obtained at 700 K through mechanical alloying. Based on the optimal BiSb(Se 0.94 Br 0.06) 3 composition, we perform percolation effect with mixed grain sizes in nanoscale and microscale to enhance carrier mobility. It is found that carrier mobility is favorably improved by the addition of microscale grains (∼30 μm) in nanostructured BiSb(Se 0.94 Br 0.06) 3 matrix due to the reduced grain boundaries to carrier scattering, which benefits high electrical conductivity and power factor. Simultaneously, the BiSb(Se 0.94 Br 0.06) 3 matrix with mixed grain sizes still maintains very low thermal conductivity due to its intrinsically strong lattice anharmonicity. Owing to the optimized electrical properties and maintained low thermal conductivity, we obtain a maximum ZT value of ∼1.0 at 700 K in BiSb(Se 0.94 Br 0.06) 3 –4C matrix with 40% microscale grains. This work provides a feasible method to optimize thermoelectric performance by designing microstructure with percolation effect. • Carrier concentration was improved to ∼1.91 × 1020 cm−3 in n -type BiSbSe 3 by Br doping. • PF max of n -type BiSbSe 3 was significantly enhanced to ∼6.0 μW cm−1 K−2 at 700 K through improving carrier mobility via utilizing percolation. • ZT max of n -type BiSbSe 3 was enhanced from ∼0.1 to ∼1.0 at 700K. [ABSTRACT FROM AUTHOR]

Chalcopyrite compounds are promising high efficient thermoelectric materials. However, the relatively high lattice thermal conductivity at modest temperatures limits their performance. Here, we investigate the lattice dynamics in a polycrystalline CuInTe 2 with a combined experimental and computational approach. The phonon dispersion and density of states are computed using the density functional theory. Raman scattering is performed to investigate the phonon dynamical properties. Together with the bulk modulus from X-ray diffraction, the mode-Grüneisen parameters are determined. The low energy B 1 1 and E2 modes characterize the weak anharmonicity, thus responsible for the high lattice thermal conductivity. Meanwhile, B 1 1 and E2 modes display energy redshift under pressure. The softening and enhanced anharmonicity of these modes naturally result in the reduction of the thermal conductivity. Our study suggests that pressure is a routine to reduce the phonon heat conduction at modest temperatures in chalcopyrites. • The phonon dispersion of CuInTe 2 is provided from the combined theoretical calculations and Raman scattering measurements. • The structural evolution of CuInTe 2 with pressure is given from high-pressure X-ray diffraction and Raman scattering measurements. • The mode-Grüneisen parameters of CuInTe 2 are obtained by combining the results from X-ray diffraction and Raman scattering measurements. [ABSTRACT FROM AUTHOR]

In this work, the thermoelectric performance of p -type PbS was boosted remarkably through Na doping and introducing Cu 2 S. Firstly, the electrical transport properties (power factor) of p -type PbS was optimized via Na doping, and the maximum ZT ∼ 0.67 was achieved in Pb 0.98 Na 0.02 S. Secondly, the total thermal conductivity of Pb 0.98 Na 0.02 S was suppressed through introducing Cu 2 S by means of significantly reducing the electronic thermal conductivity by 80% at 823 K through Cu counter-doping, meanwhile, the power factor of Pb 0.98 Na 0.02 S was further enhanced through optimizing carrier concentrations via introducing Cu. The combination of decreasing total thermal conductivities and the optimizing power factors leads to peak ZT ∼1.2 at 823 K in p -type Pb 0.98 Na 0.02 S–2%Cu 2 S. Present results illustrate that introducing Cu 2 S is an effective method to enhance the thermoelectric performance of p -type PbS through decreasing the electronic thermal conductivity which also has great potential in other thermoelectric materials system. • Thermoelectric performance of p -type PbS was remarkably boosted by reducing electronic thermal conductivity κ ele. • κ ele of p -type Pb 0.98 Na 0.02 S was reduced by 80% from ∼0.53 W m−1K−1 to ∼ 0.11 W m−1K−1 at 823 K with introducing Cu 2 S. • The maximum ZT ∼1.2 at 823 K was realized in p -type Pb 0.98 Na 0.02 S–2%Cu 2 S. [ABSTRACT FROM AUTHOR]

PbTe-based thermoelectric materials are considered to be a medium-temperature thermoelectric candidates and the high-performance n -type PbTe is urgently to be developed to match its p -type counterpart on account of practical application. Herein, we firstly optimized the carrier density of n -type PbTe through Sb doping, and obtained a maximum ZT value of ∼1.0. Then, based on the optimized carrier density, we introduced ternary compounds AgSb(Se, Te) 2 to suppress the lattice thermal conductivity. Minimum lattice thermal conductivity of n -type PbTe was reduced as low as ∼0.53 W m−1K−1 and ∼0.62 Wm−1K−1 through introducing AgSbSe 2 and AgSbTe 2 , respectively. Combining the maintained electrical properties with suppressed thermal conductivity, maximum ZT values ∼1.2 and ∼1.3 were obtained in PbTe+2%AgSbSe 2 and PbTe+2%AgSbTe 2 , respectively. This work provides an effective strategy of synergistically balancing charge and phonon transports in n -type PbTe with ternary AgSb(Se, Te) 2 compounds. • κ min of n -type PbTe was reduced to ∼ (0.53–0.62) Wm−1K−1 through introducing AgSb(Se, Te) 2. • Power factor ∼20.0 μWcm−1K−2 was realized in n -type PbTe through maintaining carrier mobility. • ZT max of n -type PbTe was enhanced from ∼1.0 to ∼ (1.17–1.25). [ABSTRACT FROM AUTHOR]