Thermoelectric power of texture revealed in SnSe
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ric power of texture revealed in SnSe
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he thermoelectric materials community has recently been turning its attention to tin selenide (SnSe), whose thermoelectric properties were generally overlooked until a record value of 2.6 for the thermoelectric figure of merit ZT, the parameter expressing the efficiency of heatto-electricity conversion, was recorded in a SnSe single crystal (Nature, doi:10.1038/
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MRS BULLETIN
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VOLUME 41 • APRIL 2016
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Scanning electron micrographs of heteroepitaxial films on diamond. Credit: Crystal Growth & Design.
fabrication costs dramatically, which is encouraging for future work. And the 0.5% mismatch is especially good—“It’s a record,” Evlashin says. The vitality of diamond electronics depends on the ability to create durable and effective metal contacts on diamond. But
this work also has applications in radiation sensing, and may have impact as far reaching as nanophotonics and quantum computing. Evlashin and colleagues have opened the door to a new avenue of research and discovery in electronic materials. Antonio Cruz
nature13184). This outstanding result was associated with structural anisotropy and the strongly anharmonic bonding that together yield an ultralow intrinsic thermal conductivity. That SnSe comprises abundant and environmentally friendly elements has further motivated the study of polycrystalline SnSe, which is better suited to industrial scale-up than single crystals. Doping and texturing have been exploited to improve the performance of polycrystalline SnSe, but early results suffered from uncertainty and failed
to deliver ZT > 1. In a recent report in the Journal of Materials Chemistry C (doi:10.1039/c6tc00204h), a team of researchers from Scotland and France have further explored the impact of texturing on the thermoelectric behavior, revealing how small regions of structural disorder dramatically affect the thermal conductivity of SnSe samples. “The optimization of the thermoelectric performance is already challenging for nominally isotropic materials, but is of even greater complexity in materials such as SnSe, where texturing
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NEWS & ANALYSIS MATERIALS NEWS is an extra degree of freedom,” says JanWillem Bos from Heriot-Watt University, UK, senior author of the study. Employing a solid-state reaction and hot-pressing, the team prepared polycrystalline pellets whose core consisted of SnSe platelets oriented at 45°, while the external regions showed increasing disorder and domains of platelets oriented perpendicular to the pressing direction. The low electrical resistivity, combined with a moderate Seebeck coefficient, yielded a power factor close to the value
reported for single crystals. The researchers calculated the thermal conductivity (κ) from measurements of thermal diffusivity and heat capacity. They found that κ parallel to the pressing direction, in samples that included the boundary regions, was appreciably lower (0.6 W m–1 K–1) than that along the perpendicular direction in core specimens (1.5 W m–1 K–1). The research
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