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      High thermoelectric performance in low-cost SnS0.91Se0.09 crystals

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          Abstract

          Thermoelectric technology allows conversion between heat and electricity. Many good thermoelectric materials contain rare or toxic elements, so developing low-cost and high-performance thermoelectric materials is warranted. Here, we report the temperature-dependent interplay of three separate electronic bands in hole-doped tin sulfide (SnS) crystals. This behavior leads to synergistic optimization between effective mass ( m*) and carrier mobility (μ) and can be boosted through introducing selenium (Se). This enhanced the power factor from ~30 to ~53 microwatts per centimeter per square kelvin (μW cm −1 K −2 at 300 K), while lowering the thermal conductivity after Se alloying. As a result, we obtained a maximum figure of merit ZT ( ZT max) of ~1.6 at 873 K and an average ZT ( ZT ave) of ~1.25 at 300 to 873 K in SnS 0.91Se 0.09 crystals. Our strategy for band manipulation offers a different route for optimizing thermoelectric performance. The high-performance SnS crystals represent an important step toward low-cost, Earth-abundant, and environmentally friendly thermoelectrics.

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              Ultralow thermal conductivity and high thermoelectric figure of merit in SnSe crystals.

              The thermoelectric effect enables direct and reversible conversion between thermal and electrical energy, and provides a viable route for power generation from waste heat. The efficiency of thermoelectric materials is dictated by the dimensionless figure of merit, ZT (where Z is the figure of merit and T is absolute temperature), which governs the Carnot efficiency for heat conversion. Enhancements above the generally high threshold value of 2.5 have important implications for commercial deployment, especially for compounds free of Pb and Te. Here we report an unprecedented ZT of 2.6 ± 0.3 at 923 K, realized in SnSe single crystals measured along the b axis of the room-temperature orthorhombic unit cell. This material also shows a high ZT of 2.3 ± 0.3 along the c axis but a significantly reduced ZT of 0.8 ± 0.2 along the a axis. We attribute the remarkably high ZT along the b axis to the intrinsically ultralow lattice thermal conductivity in SnSe. The layered structure of SnSe derives from a distorted rock-salt structure, and features anomalously high Grüneisen parameters, which reflect the anharmonic and anisotropic bonding. We attribute the exceptionally low lattice thermal conductivity (0.23 ± 0.03 W m(-1) K(-1) at 973 K) in SnSe to the anharmonicity. These findings highlight alternative strategies to nanostructuring for achieving high thermoelectric performance.
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                Author and article information

                Journal
                Science
                Science
                American Association for the Advancement of Science (AAAS)
                0036-8075
                1095-9203
                September 26 2019
                September 27 2019
                September 26 2019
                September 27 2019
                : 365
                : 6460
                : 1418-1424
                Article
                10.1126/science.aax5123
                31604269
                9a09f137-f52c-4c0a-b702-d6e26636663e
                © 2019

                http://www.sciencemag.org/about/science-licenses-journal-article-reuse

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