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2012年9月Nature关于热电材料最新文献High-performance bulk TE with 分级结构
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索引：Biswas, K., J. He, et al. (2012). "High-performance bulk thermoelectrics with all-scale hierarchical architectures." Nature 489(7416): 414-418 摘要：With about two-thirds of all used energy being lost as waste heat, there is a compelling need for high-performance thermoelectric materials that can directly and reversibly convert heat to electrical energy.However, the practical realization of thermoelectricmaterials is limited by their hitherto low figure of merit,ZT, which governs the Carnot efficiency according to the second law of thermodynamics. The recent successful strategy of nanostructuring to reduce thermal conductivity has achieved record-highZT values in the range 1.5–1.8 at 750–900 kelvin1–3, but still falls short of the generally desired threshold value of 2. Nanostructures in bulk thermoelectrics allow effective phonon scattering of a significant portion of the phonon spectrum, but phonons with long mean free paths remain largely unaffected. Here we show that heat-carrying phonons with long mean free paths can be scattered by controlling and fine-tuning the mesoscale architecture of nanostructured thermoelectric materials. Thus, by consideringsourcesof scattering on all relevant length scales in a hierarchical fashion—from atomic-scale lattice disorder and nanoscale endotaxial precipitates to mesoscale grain boundaries— we achieve the maximum reduction in lattice thermal conductivity and a large enhancement in the thermoelectric performance of PbTe. By taking such a panoscopic approach to the scattering of heatcarrying phonons across integrated length scales, we go beyond nanostructuring and demonstrate a ZT value of 2.2 at 915 kelvin in p-type PbTe endotaxially nanostructured with SrTe at a concentration of 4 mole per cent and mesostructured with powder processing and spark plasma sintering. This increase in ZT beyond the threshold of 2 highlights the role of, and need for, multiscale hierarchical architecture in controlling phonon scattering in bulk thermoelectrics, and offers a realistic prospect of the recovery of a significant portion of waste heat. 实验方法：Several samples of PbTe–SrTe(0–4 mol%) doped with 2 mol% Na were synthesized first in the form of bulk ingots by melting at 1,323K over 10 h, quenching to room temperature (297 K), followed by powder processing (Retsch RM200, Retsch GmbH) and spark plasma sintering (SPS 10-4, Thermal Technology LLC) at 823K for 10 min under an axial pressure of 60MPa in an argon atmosphere (supplementary, experimental). The s and S were measured simultaneously in a helium atmosphere at temperatures ranging from room temperature to about 923K on a ULVAC-RIKO ZEM-3 instrument system. We determined carrier concentrations using measurements of Hall coefficients at room temperature with a home-built system in applied magnetic fields ranging from 0 to 1.25 T. The thermal diffusivity, D, was directly measured in the temperature range 300–923K by using the laser flash diffusivity method in a commercial Netzsch LFA-457 instrument. The thermal diffusivity was measured along the same direction as was the electrical transport. The heat capacity, Cp, was determined on the basis of previous reported experimental literature for PbTe (refs 11, 29). The total thermal conductivity was calculated using the formula ktotal5DCpr, where r is the sample density, measured by gas pycnometer (Micromeritics AccuPyc 1340). 引文29篇。 附件2为Endnote索引。 |
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