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Energy filtering effect is usually utilized in composites to enhance the thermoelectric performance, and a reliable theoretical approach is needed to predict the optimum parameters related to this effect. By taking Bi2Te3 as an example, we show that first principles calculations and Boltzmann transport equations can be used to evaluate energy filtering effect, and the optimal values for the maximum power factor of interfacial potential barrier height ( Eb) and carrier scattering probability ( p) can be calculated precisely. The calculation results show that the power factor can be greatly enhanced at high carrier concentrations by energy filtering. This enhancement is sensitive to Eb and p: to achieve 40% power factor enhancement, Eb must be in the range 0.06-0.10 eV, and p should be greater than 60%. The optimal Eb also shows weak dependence on p. Our approach can be easily applied to other materials due to the generality of first principles calculations, and will aid high throughput screening for new thermoelectric composites. [ABSTRACT FROM AUTHOR]

This study demonstrates scalable mechanochemical synthesis of rhodostannite Cu 2 FeSn 3 S 8 nanocrystals. On the contrary to the previous reports focused on the synthesis of stannite Cu 2 FeSnS 4 reporting the rhodostannite impurity, we succeeded in preparing stannite-free product after milling. Pure elements were used for a solvent-free production in a batch of 100 g using an eccentric vibratory mill. The progress of the synthesis was monitored by X-ray diffraction and magnetometry, which both confirmed a successful reaction progress until 6 h of milling. However, further treatment (until 10 h) did not result in an improvement, as quite a high saturation magnetization (7.8 emu/g) and clearly evident diffraction at around 44° in the XRD pattern of the product due to the presence of ferromagnetic un-reacted iron with content slightly above 5% was evidenced. The product is sulfur- and tin-deficient, with crystallite size of around 12 nm. In-depth SEM/EDS analysis has shown the inhomogeneity of Fe distribution due to unfinished reaction. The bandgap of the produced material was 1.29 eV. The spark plasma sintering treatment resulted in complete consumption of non-reacted iron, but partial decomposition to stannite Cu 2 FeSnS 4 was observed. The product is an intrinsic semiconductor with high electrical resistivity, and is therefore unsuitable for thermoelectric application. However, its thermal conductivity is low, thus it could be used as an electrically and thermally insulating material. [Display omitted] • Rhodostannite Cu 2 FeSn 3 S 8 nanocrystals have been successfully produced. • Environmentally friendly solid-state mechanochemical approach has been used. • Scalability of the synthesis up to 100 g per batch was demonstrated. • The product showed interesting electrical and thermal insulating properties. [ABSTRACT FROM AUTHOR]