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High performance thermoelectric Cu 2 Te 1- x S x solid solutions can surprisingly be formed over a wide compositional range even with big atomic size difference between S and Te. The Cu sublattice has been found to be partially ordered and even shows amorphous substructures in some compositions, while S/Te is considered to form a chemically disordered yet crystalline sublattice. However, precise order-disorder configurations of cation-anion sublattices and their evolution upon compositional change still remain unclear. Meanwhile, the appearance of diffuse reflections on the electron diffraction patterns suggests occurrence of short-range order whose structures are not yet solved. Here, atomic structures of Cu 2 Te 1- x S x (x = 0.1, 0.2, 0.4, 0.5, 0.6 and 0.8) have been investigated by transmission electron microscopy in both real and reciprocal spaces. The high-angle annular dark field atomic imaging indicates an approximate hexagonal stacking for S/Te atoms in all solution compositions. However, location of Cu atoms in numerous interstices of the chalcogen sublattice varies by S/Te atomic ratio, leading to change in order-disorder configurations of Cu or even nanoscale phase separation. Diffuse scattering with different geometries are identified to arise from chemical short-range order in forms of sulphur-rich atomic layers on (0001) and lath-like tellurium aggregation on {10-10}. The as-observed compositionally tailored solid solution structures and short-range order structures are found to be strongly correlated to the electron and phonon transportation in Cu 2 Te 1- x S x. The present work indicates a promising strategy for designing solid solutions having large atomic-size mismatch which may generate abundant order/disorder atomic configurations hence greatly improve the thermoelectric properties. [Display omitted] [ABSTRACT FROM AUTHOR]

The complex doping behavior of Ga and In in CoSb 3 has been investigated using ab initio total-energy calculations and thermodynamics. The formation energies of void filling, Sb substitution and complex dual-site occupancy defects with different charge states, and their dependence on chemical potentials of species, were studied. Results show that Ga predominantly forms dual-site 2Ga VF –Ga Sb defects and substitutes for Sb only at very high Fermi levels or electron concentrations. In, on the other hand, can play multiple roles in skutterudites, including filling in the crystalline voids, substituting for Sb atoms or forming dual-site occupancy, among which the fully charge-compensated dual-site defects (2In VF –In Sb and 4In VF –2In Sb ) are dominant. The equilibrium concentration ratio of impurities at void-filling sites to those at Sb-substitution sites for Ga-doped CoSb 3 is very close to be 2:1, while this value markedly deviates from 2:1 for In-doped CoSb 3 . The 2:1 ratio of Ga doping in CoSb 3 leads to low electron concentration (∼2 × 10 19 cm −3 ) and makes the doped system a semiconductor. [ABSTRACT FROM AUTHOR]

Lanthanum telluride (La 3- x Te 4) is one of the important candidates of thermoelectric (TE) materials working at high temperatures over 1000 K. However, the thermal stability and oxidation resistance of the TE materials become the crucial issue when they are working at so high temperatures. In this report, it is found that, although La 3- x Te 4 exhibits excellent thermal stability up to 1200 K under inert atmosphere, the existence of oxygen even in very low partial pressure causes serious oxidation and performance degradation at a temperature over 700 K. By introducing metallic nickel particles into La 2.74 Te 4 matrix forming La 2.74 Te 4 /Ni composites, the oxidation rate is greatly reduced both in air and low oxygen partial pressure (Po 2 = 10−3 MPa). The dense La 2 NiO 4 /Ni 2 Te 3 O 8 /NiO oxide composite layer formed during oxidation is in charge of "blocking" the diffusion of oxygen. Dispersing Ni particles gives indistinct influence on the thermoelectric properties leading to a good dimensionless thermoelectric figure of merit as 1.0 at 1273 K in the La 2.74 Te 4 /10 vol.% Ni composite. [Display omitted] [ABSTRACT FROM AUTHOR]

Thermoelectric materials require not only high performance to maximize the energy conversion efficiency but also good mechanical properties to guarantee machinability and reliable operation. It is usually hard to embrace both at once. Herein, we demonstrated the entropy engineering as a promising avenue to realize both exceptional thermoelectric performance and robust mechanical properties in multicomponent alloys Cu 2- y Ag y Te 1-2 x S x Se x. Entropy engineering by mixing multiple elements stabilizes the high-symmetry hexagonal structure, extends the solubility limit of Ag, and concurrently lessens the phase transition numbers. Furthermore, with co-alloying of S/Se and Ag in Cu 2 Te, the carrier concentration is largely reduced while the effective mass is enhanced, yielding higher Seebeck coefficient and power factor. Owing to the strong phonon scattering by lattice disorder, the thermal conductivity is decreased by one order of magnitude, reaching 0.29 W m−1 K−1 at room temperature, which is even lower than the amorphous limit. A state-of-the-art peak zT of 1.4 and average zT of 0.74 are achieved in Cu 1.9 Ag 0.1 Te 0.6 S 0.2 Se 0.2. Moreover, the mechanical properties are significantly improved in virtue of the entropy engineering strengthening effect, making it more promising for thermoelectric applications. Record-high average zT of 0.74 and remarkably improved compressive strength were achieved in multicomponent alloys Cu 2- y Ag y Te 1-2 x S x Se x through entropy engineering [Display omitted]. [ABSTRACT FROM AUTHOR]

Abstract: P-type compounds Cu2Ga x Sn1 − x Se3 (x =0.025, 0.05, 0.075) with a diamond-like structure were consolidated using hot pressing sintering (HP) and spark plasma sintering (SPS) techniques. High-temperature thermoelectric properties as well as low-temperature Hall data are reported. Microstructural analysis shows that the distribution of Ga is homogeneous in the samples sintered by HP but inhomogeneous in the samples sintered by SPS, even with an electrically isolating and thermally conducting BN layer during the sintering. The Seebeck coefficients of the samples sintered by HP and SPS show similar dependence on the carrier concentration and are insensitive to the composition inhomogeneity. In contrast, the composition inhomogeneity results in lower carrier mobility and thus lower electrical conductivity in the samples sintered by SPS than those sintered by HP. Lattice thermal conductivity is further reduced through Ga doping; however, this effect is weakened by the inhomogeneous distribution of Ga. Due to their larger carrier mobility and lower lattice thermal conductivity, the samples sintered by HP exhibit 15–35% higher thermoelectric figure of merits (ZT) than those SPS samples with a high Ga doping level and without the coated BN layer, in which the composition homogeneity is worse. A ZT value of 0.43 is obtained for the HP Cu2Ga0.075Sn0.925Se3 sample at 700K. [Copyright &y& Elsevier]

Abstract: Reversible electrochemical lithium intercalation/deintercalation reactions have been applied to integrally modify the thermoelectric performance of Bi2Se0.3Te2.7 compounds. The carrier concentration of Bi2Se0.3Te2.7 has been precisely controlled experimentally through the adjustment of the residual lithium content. The variations of electronic transport properties of Li x Bi2Se0.3Te2.7, including electrical conductivity, Seebeck coefficient and carrier concentration, as a function of the intercalated lithium amount (x), show a special non-monotonic P-type to N-type doping trend. This variation is caused by the competition of two mechanisms controlling the carrier concentration: (i) decreasing of the Se/Te ratio through a Li–Se reaction that reduces the amount of the TeBi or SeBi antisite defects and therefore the electron concentration; (ii) n-type doping by lithium that provides the electron. Moreover, the nanoparticle exfoliation during lithium intercalation and deintercalation reactions leads to the formation of an internal nanocrystalline composite structure which effectively reduces the lattice thermal conductivity. Through an integral modification of both electrical and thermal transport properties, the maximum ZT value of Li x Bi2Se0.3Te2.7 was improved by nearly 25%. [Copyright &y& Elsevier]

Abstract: n-type filled skutterudite Yb0.26Co4Sb12 composites in which p-type GaSb nanostructured inclusions (5–20nm) were dispersed were fabricated by an in situ method involving the introduction of metastable void-filling impurity Ga and enrichment of Sb in the synthesis procedure. With the homogeneously dispersed GaSb nanoinclusions, which probably result from the scattering of low-energy electrons by the GaSb-related boundary energy barriers, the power factor is enhanced due to the significant enhancement of the Seebeck coefficient. The total thermal conductivity was decreased with the depression of electronic thermal conductivity. As a result, the dimensionless thermoelectric figure of merit ZT value was improved over a wide working temperature range of 300–850K, and the expected optimal thermal-electric conversion efficiency ηopt 15.0% was obtained for the Yb0.26Co4Sb12/0.2GaSb nanocomposite. [Copyright &y& Elsevier]