bd p-Type PbTe is an outstanding high temperature thermoelectric material with zT of 2 at high temperatures due to its complex band structure which leads to high valley degeneracy. Lead-free SnTe has a similar electronic band structure, which suggests that it may also be a good thermoelectric material. However, stoichiometric SnTe is a strongly p-type semiconductor with a carrier concentration of about 1 Â 10 20 cm À3 , which corresponds to a minimum Seebeck coefficient and zT. While in the case of p-PbTe (and n-type La 3 Te 4 ) one would normally achieve higher zT by using high carrier density in order to populate the secondary band with higher valley degeneracy, SnTe behaves differently. It has a very light, upper valence band which is shown in this work to provide higher zT than doping towards the heavier second band. Therefore, decreasing the hole concentration to maximize the performance of the light band results in higher zT than doping into the high degeneracy heavy band. Here we tune the electrical transport properties of SnTe by decreasing the carrier concentration with iodine doping, and increasing the carrier concentration with Gd doping or by making the samples Te deficient. A peak zT value of 0.6 at 700 K was obtained for SnTe 0.985 I 0.015 which optimizes the light, upper valence band, which is about 50% higher than the other peak zT value of 0.4 for Gd z Sn 1ÀzT e and SnTe 1+y which utilize the high valley degeneracy secondary valence band.

Solid solution is a potential way to optimize thermoelectric performance for its low thermal conductivity compared to those of the constituent compounds because of the phonon scattering from disordered atoms. Tin(II) sulfide (SnS) shows analogous band structure and electrical properties with tin selenide (SnSe), which was the motivation for investigating the thermoelectric performance of SnS and SnS-SnSe solid solution system. SnS compound and SnS 1Àx Se x (0 < x < 1) solid solution were fabricated using the melting method and they exhibited anisotropic thermoelectric performance along the parallel and perpendicular to the pressing directions. For the SnS compound, the maximum zT k value is 0.19 at 823 K along the parallel to pressing direction, which is higher than that along the perpendicular to the pressing direction (zT t ¼ 0.16). The zT values of SnS 0.5 Se 0.5 and SnS 0.2 Se 0.8 were higher than those of the SnS compound and a maximum zT value of 0.82 was obtained for SnS 0.2 Se 0.8 at 823 K, which is more than four times higher than that of SnS.

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Abstract. Elemental carbon (EC) is a collective term encompassing all thermally altered carbonaceous materials and can be subdivided into two classes: char and soot. Since the different classes of EC have different chemical and physical properties, their optical light-absorbing properties differ, so that it is essential to differentiate them in the environment. One year of observations of the daily and seasonal variations of carbonaceous particles were conducted in Xi'an, China in 2004 to demonstrate the different characteristics of char and soot in the atmosphere. Total carbon (TC), organic carbon (OC), EC and char-EC showed similar seasonal trends, with high concentrations in winter and low concentrations in summer, while soot-EC revealed relatively small seasonal variations, with maximum concentration (1.85 μg m−3) in spring and minimum concentration (1.15 μg m−3) in summer. The strong correlation between EC and char-EC (R2=0.99) indicates that previously reported total EC reflected the characteristics of char only, while overlooking that of soot. However, soot exhibits stronger light-absorbing characteristics than char, and merits greater focus. The small seasonal variation of soot-EC indicates that soot may be the background fraction in total EC, and is likely to have an even longer lifetime in the atmosphere than previously estimated for total EC, which suggests that soot has a greater contribution to global warming. Although char-EC/soot-EC ratio is similar to primary OC/EC ratio as both vary with emission sources, OC/EC ratio is affected by the secondary organic aerosol (SOA) formation. Thus char-EC/soot-EC may be a more effective indicator than OC/EC in source identification of carbonaceous aerosol. Comparison of seasonal variations of OC/EC and char-EC/soot-EC ratios in Xi'an confirms this point. However, wet scavenging by snow and rain was more effective for char than for soot and influenced the char-EC/soot-EC ratio, and this factor should be considered in source identification as well.

Dense bulk samples of (Ag,In)‐co‐doped Cu2SnSe3 have been prepared by a fast and one‐step method of combustion synthesis, and their thermoelectric properties have been investigated from 323 to 823 K. The experimental results show that Ag‐doping at Cu site remarkably enhances the Seebeck coefficient, reduces both electrical and thermal conductivities, and finally increases the figure of merit (ZT) value. The ZT of the Cu1.85Ag0.15SnSe3 sample reaches 0.80 at 773 K, which is improved by about 70% compared with the unadulterated sample (ZT = 0.46 at 773 K). First principle calculation indicates that Ag‐doping changes the electronic structure of Cu2SnSe3 and results in larger effective mass of carriers, thus enhancing the Seebeck coefficient and reducing the electrical conductivity. The low electrical conductivity caused by Ag‐doping can be repaired by accompanying In‐doping at Sn site, and by (Ag,In)‐co‐doping the thermoelectric properties are further promoted. The (Ag,In)‐co‐doped sample of Cu1.85Ag0.15Sn0.9In0.1Se3 shows the maximum ZT of 1.42 at 823 K, which is likely the best result for Cu2SnSe3‐based materials up to now. This work indicates that co‐doping may provide an effective solution to optimize the conflicting material properties for increasing ZT.

In the pursuit of low thermal conductivity materials for thermal management, one always tries to increase the material entropy by increasing the number of components in the materials to scatter heat‐carrying phonons. However, it also drastically increases the technological complexity to synthesize materials with the target complex composition. Here, a material family is presented with simple composition Ln3NbO7, which only contains binary oxides of Ln2O3 (Ln = Dy, Er, Y, Yb) and Nb2O5. The thermal conductivities approach the theoretical minimum limit, where the large chemical inhomogeneity due to the charge disorder and fluctuation of bonding length in Ln3NbO7 plays a major role. Despite the simple composition, Ln3NbO7 demonstrates an unprecedentedly high scattering rate of vibration states, as confirmed by the highest elastic constant/thermal conductivity ratio, as well as the diffused wavevector‐frequency dispersion. In contrast to the conventional wisdom that low thermal conductivity materials should be explored in the pool of “complex” multiple‐component materials, this work points out an avenue to look into materials with simple composition but large internal chemical inhomogeneity, which would be of both scientific and technological significance in the fields of thermal barrier coating, thermoelectric materials, etc.

Lead-free polycrystalline SnSe is a promising thermoelectric compound consisting of earth-abundant elements.

The La(Fe,Si)13‐based compounds have been recently developed as promising negative thermal expansion (NTE) materials by elemental substitution, which show large, isotropic and nonhysteretic NTE properties as well as relatively high electrical and thermal conductivities. In this paper, the La(Fe,Si)13 hydrides are prepared by a novel electrolytic hydriding method. Furthermore, the thermal expansion and magnetic properties of La(Fe,Si)13 hydrides are investigated by the variable‐temperature X‐ray diffraction and physical property measurement system. Fascinatingly, it is found that room‐temperature NTE properties and zero thermal expansion (ZTE) properties with broad operation‐temperature window (20–275 K) have been achieved after electrolytic hydriding. The further magnetic properties combined with theoretical analysis reveal that the improvements of NTE and ZTE properties in the La(Fe,Si)13 hydrides are ascribed to the variations of magnetic exchange couplings after hydrogenation. The present results highlight the potential applications of La(Fe,Si)13 hydrides with room‐temperature NTE and broad operation‐temperature window ZTE properties.