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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.

The effects of Ag nanoinclusions on thermoelectric properties of Ag 2 S semiconducting nanostructures, synthesized by a novel one-pot facile polyol method, have been investigated. The resulting products are characterized by powder XRD, EDAX, XPS, and UV−vis techniques. FESEM images reveal the formation of disc-shaped Ag 2 S nanoparticles with an average thickness of 52 nm and diameters ranging from 50 nm to a few hundreds of nm. All samples show a systematic reduction in electrical resistivity with increasing Ag content in the composites. The Seebeck coefficient (α) values for the Ag nanoparticle-incorporated Ag 2 S nanocomposites are notably high near 300 K because of the low-energy charge-carrier filtering effect, which is due to preferential scattering of low-energy electrons at the barrier potentials set up at metal−semiconductor interfaces. The theoretical fitting of α data reveals a systematic shift of the Fermi level toward the conduction band edge with increasing Ag content in the composites. A significantly improved thermoelectric power factor at 325 K is observed for a wide range of Ag nanoinclusions with the highest ZT of 0.0029 at 325 K in the Ag 2 S−Ag nanocomposite with 20.1% Ag.

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The total spectral weight S of the emergent low-energy quasipaticles in high-temperature superconductors is explored by x-ray absorption spectroscopy. In order to examine the applicability of the Hubbard model, regimes that cover from zero doping to overdoping are investigated. In contrast to mean field theory, we found that S deviates from linear dependence on the doping level p. The slope of S versus p changes continuously throughout the whole doping range with no sign of saturation up to p = 0.23. Therefore, the picture of Zhang-Rice singlet remains intact within the most prominent doping regimes of HTSC's.