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We report the effect of Al substitution on the temperature-dependent electrical resistivity, Seebeck coefficient, as well as thermal conductivity in the binary compound cobalt monosilicide. It is found that the substitution of Al onto the Si sites causes a dramatic decrease in the electrical resistivity and lattice thermal conductivity. A theoretical analysis indicated that the reduction of lattice thermal conductivity arises mainly from point-defect scattering of the phonons. For xу0.05 in the CoSi 1Ϫx Al x system, the Seebeck coefficient changes sign from negative to positive, accompanied by the appearance of a broad maximum. These features are associated with the change in the electronic band structure, where the Fermi level shifts downwards from the center of the pseudogap due to hole-doping effect. While the thermoelectric performance improves with increasing Al substitution, the largest figure-of-merit ZT value among these alloys is still an order of magnitude lower than the conventional thermoelectric materials.

We report the first thermoelectric properties of CuAgS, x = 0-0.75 nanocomposites, synthesized by using a facile polyol method. Systematic characterizations using powder XRD, Rietveld refinement of XRD, EDAX, XPS and Raman spectroscopy confirmed their single phase, hexagonal crystal structure with the space group P6/mmc, nominal elemental composition, valence states of the constituent elements and stoichiometric nature. The TEM images showing the CuS formation of nearly perfect hexagonal disk-like particles of average thickness 26.7 nm and breadth ranging in a few hundreds of nanometers with nanorods stacked from these hexagonal nanodisks (NDs) elongated along the c axis corroborate the FESEM images. Attributed to structural phase transition, an anomaly at 55 K is clearly observed in both the thermopower and Hall resistivity data. By increasing x, a systematic reduction in thermal conductivity was observed near 300 K. Consequently, a 50% enhancement in figure of merit was observed for CuAgS as compared to pure CuS at 300 K. These results therefore are expected to provide a new direction in improving ZT near 300 K.

We report the results of the Y substitution in Sr 1−x Y x Si 2 with x Յ 0.15 via measuring the temperature-dependent electrical resistivity, thermal conductivity, as well as Seebeck coefficient. Upon substituting Y onto the Sr sites, the electrical resistivity exhibit semiconducting behavior and the room-temperature electrical resistivity tends to reduce for x Յ 0.08. The thermal conductivity also decreases with increasing the Y content. Moreover, the Seebeck coefficient has a substantial increase and a maximum of about 220 V / K at around 80 K has been found for x = 0.08. These promising effects lead to a significant enhancement in the thermoelectric performance characterized by the figure-of-merit, ZT. A room-temperature ZT value of approximately 0.4 is thus achieved for Sr 0.92 Y 0.08 Si 2 , about one order of magnitude larger than that of stoichiometric SrSi 2 .

We studied the defects of Bi2Se3 generated from Bridgman growth of stoichiometric and nonstoichiometric self-fluxes. Growth habit, lattice size, and transport properties are strongly affected by the types of defect generated. Major defect types of BiSe antisite and partial Bi2-layer intercalation are identified through combined studies of direct atomic-scale imaging with scanning transmission electron microscopy (STEM) in conjunction with energy-dispersive X-ray spectroscopy (STEM-EDX), X-ray diffraction, and Hall effect measurements. We propose a consistent explanation to the origin of defect type, growth morphology, and transport property.