Search

Ta-doped Ti1-xTaxCoSb (0≤x≤0.08) half-Heusler compounds were synthesized by melting and annealing process. Their thermoelectric properties were studied in the temperature range of 300–900 K. The Ti1-xTaxCoSb compounds exhibit negative Seebeck coefficients with considerably large absolute values. With increasing Ta substitution, the electrical conductivity was greatly increased, but the thermal conductivity was reduced. Because of the combined effects of increased electrical conductivity and reduced thermal conductivity, the thermoelectric performance of Ti1-xTaxCoSb alloys was apparently improved by doping Ta. The dimensionless figure of merit of 0.3 was obtained for Ti0.92Ta0.08CoSb compound at 900 K. This value is about ten times larger than that of the undoped TiCoSb compound. [ABSTRACT FROM AUTHOR]

Abstract: n-Type (Bi2Te3)0.93(Bi2Se3)0.07 thermoelectric materials doped with various content of TeI4 (0, 0.05, 0.10, 0.13, and 0.15wt.%) have been fabricated through the zone melting method. Electrical conductivity (σ), Seebeck coefficient (α) and thermal conductivity (κ) were measured along the crystal growth direction in the temperature range of 300–500K. The influence of the variations of TeI4 content on thermoelectric properties was studied. The undoped (Bi2Te3)0.93(Bi2Se3)0.07 exhibited p-type conduction and it translated to n-type when TeI4 was doped. The increase of TeI4 content increased the carrier concentration and thus resulted in an increase of σ and a decrease of |α|. The maximum figure of merit ZT (ZT=α2σT/κ) of the zone-melted crystals in the direction parallel to the growth direction showed a value of 0.90 for the sample containing 0.10wt.% TeI4. [Copyright &y& Elsevier]

Abstract: In the present study, p-type (Bi2Te3) x (Sb2Te3)1− x crystals with various chemical compositions (, 0.05, 0.10, 0.16, 0.20, 0.24 and 0.26) were fabricated through the zone melting method. Thermoelectric properties, including Seebeck coefficient (), electrical conductivity () and thermal conductivity (), were measured in the temperature range of 300–500K. The influence of the variations of Bi2Te3 content () on the thermoelectric properties was studied. The increase of Bi2Te3 content () caused a decrease in hole concentration and thus a decrease of and an increase of . The maximum figure of merit () of 1.14 was obtained at about 350K for the composition of 24% Bi2Te3–76% Sb2Te3 with 3wt% excess Te. [Copyright &y& Elsevier]

Abstract: The n-type Bi2(Te,Se)3 thermoelectric materials with preferred grain orientation have been fabricated through the spark plasma sintering (SPS) technique. The c-axis of the grains in the sintered samples were preferentially oriented parallel to the pressing direction, the orientation factor of the (00 l) planes changed from 0.4 to 0.85 with the sintering conditions. The anisotropy was investigated by measuring the electrical conductivities in the two directions perpendicular and parallel to the pressing direction. The optimal figure of merit ZT (ZT = α 2 σT/κ) of the sintered materials in the direction perpendicular to the pressing direction was comparative to that of the zone-melted materials in the same crystallographic direction, while the bending strength reached about 80MPa, which is 7–8 times of that of the zone-melted materials. [Copyright &y& Elsevier]

Abstract: In the present study, p-type (Bi,Sb)2Te3 thermoelectric materials have been fabricated through the spark plasma sintering (SPS) method by using powders with various particle sizes. Electrical conductivity (σ), Seebeck coefficient (α), and thermal conductivity (κ) were evaluated in the temperature range of 300–500K. The effect of annealing of the sintered samples on thermoelectric properties was also investigated. The maximum figure of merit ZT (ZT = α2σT/κ) of the sintered samples in the direction perpendicular to the pressing direction (with c-axis preferred orientation) was 1.15 at about 350K, corresponding to be about 115% of that of the zone-melted ingot with the same composition in the same crystallographic orientation; while the bending strength was highly improved from about 10 to 80MPa. [Copyright &y& Elsevier]

Ca3-xDyxCo4O9+δ (x=0, 0.15, 0.3 and 0.45) polycrystalline samples have been prepared using a sol–gel process followed by SPS sintering. Their thermoelectric properties have been carefully studied from room temperature to 1000 K. The substitution of Dy for Ca results in increasing of both thermopower and electrical resistivity, which could be attributed to the decreasing of carrier concentrations. The Dy substituted samples (x=0, 0.3) have lower thermal conductivity than Ca3Co4O9+δ due to their lower electronic and lattice thermal conductivities. The dimensionless figure of merit ZT reaches 0.27 at 1000 K for the sample of Ca2.7Dy0.3Co4O9+δ. [Copyright &y& Elsevier]

The skutterudite/electrode thermoelectric joints were fabricated with the insertion of Ti foil by spark plasma sintering. The interfacial microstructure and reliability of joints were studied during thermal duration test. A multilayer structure, which was composed of intermetallic compounds, was observed at the CoSb3/ Ti interface after thermal aging of 20 days. The interfacial reactions and diffusion path between CoSb3 and Ti were discussed. The contact resistance of CoSb3/electrode junction was measured through four-probe method and the thermal contact resistance was calculated based on multilayer mode measurement. Effects of the contact resistivity on the performance of CoSb3-based device were discussed. [ABSTRACT FROM AUTHOR]

Abstract: Polycrystalline (Fe1−x Co x )2VAl (0≤ x ≤0.5) alloys were synthesized through a combined process of arc-melting, annealing and sintering. Thermoelectric properties were investigated from 300 to 850K. Stoichiometric Fe2VAl exhibited p-type conduction, however, it shifted to n-type with slight Co substitution for Fe site. After Co substitution, the electrical conductivity and absolute value of Seebeck coefficient at room temperature increased from 1.2×105 to 5×105 Sm−1 and 30 to 112μV/K, respectively. Meanwhile, the lattice thermal conductivity dropped from 23 to 6W/mK because of the introduction of extra phonon scattering due to alloying effect. The highest dimensionless figure of merit ZT value for (Fe0.7Co0.3)2VAl is 0.09 at 650K. [Copyright &y& Elsevier]

Abstract: TiCoSb-based half-Heusler compounds were prepared by solid-state reaction and their thermoelectric properties were studied. The un-doped TiCoSb compound shows n-type conduction and demonstrates high Seebeck coefficient at high temperatures. The partial substitution of Co by Ni caused great increase in electron concentration and electrical conductivity, while the Seebeck coefficient and the thermal conductivity showed little change when Ni content (x) is below 5%. A maximum power factor of 16μW/K2 cm and a maximum dimensionless figure of merit (ZT) of 0.27 have been obtained for the composition of TiCo0.95Ni0.05Sb at 900K. [Copyright &y& Elsevier]

Thermoelectric technology generates electricity from waste heat, but one bottleneck for wider use is the performance of thermoelectric materials. Manipulating the configurational entropy of a material by introducing different atomic species can tune phase composition and extend the performance optimization space. We enhanced the figure of merit (zT) value to 1.8 at 900 kelvin in an n-type PbSe-based high-entropy material formed by entropy-driven structural stabilization. The largely distorted lattices in this high-entropy system caused unusual shear strains, which provided strong phonon scattering to largely lower lattice thermal conductivity. The thermoelectric conversion efficiency was 12.3% at temperature difference DT = 507 kelvin, for the fabricated segmented module based on this n-type high-entropy material. Our demonstration provides a paradigm to improve thermoelectric performance for high-entropy thermoelectric materials through entropy engineering. [ABSTRACT FROM AUTHOR]

TiCoSb-based half-Heusler compounds have been prepared and their thermoelectric properties are studied. By isoelectronic alloying on the Ti site with Zr, although both the thermal conductivity and electrical conductivity are suppressed, the Seebeck coefficient is improved remarkably with a highest value of -420 μV/K for Ti0.5Zr0.5CoSb at 600 K, which provides a larger space to optimize the thermoelectric performance. To further improve the performance of the TiCoSb-based isoelectronic alloy, doping Ni on the Co site was explored. It is found that small amount of Ni doping results in a great increase in the electrical conductivity, still with a relative large Seebeck coefficient. Ti0.6Hf0.4Co0.87Ni0.13Sb sample exhibits a peak power factor of 23.4 μW/cm K2, which is the highest value for n-type TiCoSb-based half-Heusler compounds reported so far. As a result, a maximum dimensionless figure of merit of 0.70 has been achieved at 900 K for Ti0.6Hf0.4Co0.87Ni0.13Sb. [ABSTRACT FROM AUTHOR]

Pseudo-binary GeSbTe alloys, best known as phase-change materials, are quasi-two-dimensional semiconductors in their stable trigonal phases with high electrical conductivity and low thermal conductivity, but their thermoelectric properties have not been systematically investigated. Here, in this letter, we prepared polycrystalline Ge2Sb2Te5, GeSb2Te4, and GeSb4Te7 bulk materials and studied the thermoelectric transport properties. Large anisotropy in Seebeck coefficient as well as in electrical conductivity is observed, which is not commonly reported in polycrystalline thermoelectric materials. Combining experimental study and theoretical calculations, one can find that this phenomenon is attributed to the asymmetry of a material's band structure. Maximal zT values of 0.46–0.60 are achieved at 750 K, indicating that GeSbTe-based compounds are promising thermoelectric materials for mid-temperature applications. [ABSTRACT FROM AUTHOR]

Abstract PEDOT:PSS coated Te (PC Te) nanorod/PEDOT:PSS composite films were prepared by a drop-casting technique. H 2 SO 4 treatment was employed to enhance thermoelectric (TE) properties of the composite films. The addition of PC Te nanorods increased both the electrical conductivity and the Seebeck coefficient of the composite films. An optimized power factor of 141.9 μW/mK2 was obtained for the film containing 90 wt% PC Te nanorods treated with 12 M H 2 SO 4 at room temperature, which was 2.75 times as high as that of the untreated composite film, corresponding to the electrical conductivity and Seebeck coefficient of 204.6 S/cm and 83.27 μV/K, respectively. XPS and GIWAXS analysis revealed the removal of insulating PSS units and the rearrangement of PEDOT chains after the H 2 SO 4 treatment. Finally, a 9-leg TE generator prototype was fabricated using the optimized composite film. The maximum output power and area output power density produced from the prototype were 47.7 nW and 57.2 μW/cm2, respectively, at the temperature difference of 40 K. Graphical abstract Image 1 Highlights • PEDOT:PSS coated Te (PC Te) nanorods were synthesized. • PC Te/PEDOT:PSS composite films were prepared by a drop-casting method. • H 2 SO 4 treatment was used to enhance TE properties of the composite films. • An optimized power factor of 141.9 μW/mK2 was obtained. • A flexible thermoelectric generator prototype was fabricated using the optimized film. [ABSTRACT FROM AUTHOR]

Abstract Herein, we demonstrate a concept of making flexible thermoelectric (TE) generators by applying cotton thread as the platforms for poly(3-hexylthiophene) (P3HT) and Argentum (Ag) paste through selectable coating method. The coated thermoelectric cotton thread can be sewed on the flexible fabrics with different knitting pictures and form thermoelectric devices. The most important is that the temperature gradient of the device was in the direction of cross-plane of the flexible fabrics, that is, between the inner and outer surfaces of clothing, therefore the flexible device can be easily wore on the body since the temperature gradient between the human body and surrounding environment is in the cross-plane direction. The maximum output power of the device with thirteen P N type legs reached 1.15 μW at a temperature gradient of 50 K when the load resistance matched the resistance of the module. Cotton-based TE device coated with P3HT may be useful for the development of self-powered wearable electronics. Highlights • Thermoelectric (TE) cotton thread was obtained through selectable coating method. • Poly(3-hexylthiophene) and Argentum paste was sequentially spaced as p-type leg and n-type leg. • Temperature gradient (ΔT) of the TE device was in the cross-plane direction. • Output power of the flexible TE device reached 1.15 μW at ΔT = 50 K. [ABSTRACT FROM AUTHOR]

Poly(3‐hexylthiophene) (P3HT) films with various molecular weights (MWs) were successfully prepared, and both their molecular structures and thermoelectric (TE) properties were investigated. It was found that the molecular weight of P3HT had an important effect on the carrier‐transport properties by affecting the molecular structure and, as a result, also had an effect on the TE performance. The electrical conductivity of the P3HT films first increased upon increasing the molecular weight and then decreased at high molecular weights, whereas the Seebeck coefficient remained at the same level. As a result, the P3HT‐M50k (MW≈50 000 g mol−1) film reached an electrical conductivity of (103.8±1.2) S cm, which is more than 20 times higher than the electrical conductivity of P3HT‐M10k (MW≈10 000 g mol−1) and almost 30 % higher than the electrical conductivity of P3HT‐M100k (MW≈100 000 g mol−1). Consequently, the maximum TE power factor of P3HT‐M50k at room temperature was as high as (22.6±0.6) μW mK−2, which is much higher than that of either P3HT‐M10k or P3HT‐M100k. Microstructure analysis combined with C‐AFM suggested that carrier transport between most of the ordered and amorphous regions was unconnected in films with low molecular weights, and this resulted in a high migration barrier and poor carrier mobility. Upon increasing the molecular weight, the long molecular chain provided enough connectivity for the charge to move through the ordered regions, which decreased the carrier barrier and increased carrier mobility. Therefore, both the conductivity and Seebeck coefficient were significantly improved. However, a too‐high molecular weight could cause more folding of the polymer chain, which would deteriorate the electrical‐transport properties. The experimental results not only reveal the intrinsic effect of molecular weight on the electric transporting properties of conducting polymers but also suggest that molecular‐weight engineering is an effective way to design and screen high‐performance polymer TE materials. Weight problem: Poly(3‐hexylthiophene) (P3HT) films with various molecular weights are successfully prepared, and both their molecular structures and thermoelectric (TE) properties are investigated. The molecular weight of P3HT is found to have an important effect on the carrier‐transport properties by affecting the molecular structure and, as a result, also has an effect on the TE performance. [ABSTRACT FROM AUTHOR]

The intrinsic ultra-low lattice thermal conductivity ( κ L ) of high performance thermoelectric Cu 2 S may arise from its multiform complex crystal structures while the further sharp drop of κ L observed at elevating temperatures close to the phase transition to hexagonal high-chalcocite is of considerable interest. In this work, in-depth in-situ transmission electron microscopy investigations have been performed by either heating or electron irradiation to analyze the structural evolution of Cu 2 S. Multiple including new phase structures have been observed in Cu 2 S. Upon increasing the temperature, drastic structural changes took place including phase transition among different phases, formation of an intermediate phase, switching of crystal orientation and inverse phase transitions, which indicate multiple forms of Cu ordering with high temperature-sensitivity. Such tremendous structural evolution along with formation and movement of phase boundaries are believed to strongly scatter the phonons. [ABSTRACT FROM AUTHOR]

Abstract: Conventional syntheses of polymer–inorganic composite thermoelectric materials suffer major problems such as inhomogeneity, large particle size, and oxidation that result in ineffective loading. Now a one‐step synthesis can be used to fabricate high‐quality small‐sized anions codoped poly(3,4‐ethylenedioxythiophene):dodecylbenzenesulfonate/Cl‐tellurium (PEDOT:DBSA/Cl‐Te) composite films using a series of novel TeIV‐based oxidants. The synchronized production of PEDOT and Te results in thick and homogeneous films containing evenly distributed and well‐protected Te quantum dots. Owing to the heavily doped crystalline polymer matrix as well as the <5 nm unoxidized Te quantum dot loading, at low Te concentrations as 2.1–5.8 wt %, the films exhibits high power factors of about 100 μW m−1 K−2, which is 50 % higher compared to a pure PEDOT:DBSA film. [ABSTRACT FROM AUTHOR]

Polymer/carbon nanotube composites have gained great progress in the past decade. However, the lack of scalability of production due to the relatively high volatility and strong toxicity of the dispersion solvent have created a great need for environmental friendly process for expanding TE applications. In this work, organic-inorganic composite films composed of a novel hydrophilic pyridinium salt polymer (noted as P2 ) and SWCNTs were prepared for thermoelectric application. The novel hydrophilic pyridinium salt polymer was designed and synthesized containing the pyridinium salt for aqueous dissolution and thiophenes as the conjugation group to make the polymer/CNT composite film electrical connecting, therefore improving the thermoelectric performance. Another pyridinium salt polymer (noted as P1 ) without thiophene group was also synthesized for the purpose of comparison. The polymers attach on the surface of CNTs through π-π conjugation interaction between conjugation groups and π-electrons of CNTs. The P2/CNT composites were homogeneously dispersed in the aqueous solution, revealing better dispersion behavior than P1/CNT , which is probably because of the stronger contact interaction between P2 /CNT than P1 /CNT due to the higher electron delocalization of polymer P2 than P1 . The electrical conductivity of P2 /CNT composite film reached the maximum value of 159 S/cm with 50% CNT content. Consequently, a high power factor of 46.4 μW/mK 2 was obtained for the P2 /50%CNT composite film. [ABSTRACT FROM AUTHOR]

The anisotropy in thermoelectric properties of three-dimensional carbon nanotubes (CNTs) and CNT/polyaniline (PANI) composites have been studied by utilizing an orderly aligned CNT arrays with a self-sustained construction. In the length direction of CNT, the electrical conductivity of the CNT array is ∼5 times larger as compared to the direction vertical to the alignment of CNTs, while the difference in thermal conductivity between these two directions is ∼25 times. As a result, strong anisotropic thermoelectric transportation has been also observed in the composites composed of PANI and CNT arrays. An enhanced thermopower in the composites, as compared to the pure PANI or CNTs, is only observed in the direction along the CNTs. This study helps the fundamental understanding on the un-conventional improved thermopower, which is more likely to be realized via adjusting the carrier transportation within the interface between CNTs and PANI rather than across it. [ABSTRACT FROM AUTHOR]

The interfacial stability of thermoelectric (TE) joints is among the key issues determining the durability of thermoelectric generators (TEGs) in practical operation. For skutterudite (SKD) based TEGs, the inter-diffusion between the metal electrode and the SKD material at high temperature plays a vital role on the interfacial stability of the joints. In this work, we report the evolution of the interfacial microstructure and the interfacial contact resistivity for a series of p-type SKD TE joints (Ti/Ce y Fe x Co 4 -x Sb 12 , x = 1.5–4, y = 0.35–1) at high temperature. The growth of the intermetallic compound (IMC) layers at the interface of all the joints was found to be controlled by the diffusion process. In contrast to the binary Ti/CoSb 3 joints, the growth of the interfacial IMC layers in the p-type Ti/Ce y Fe x Co 4 -x Sb 12 joints was considerably depressed. Moreover, no brittle TiCoSb phase was formed at the interface of the p-type joints, which resulted in good stability of the interfacial contact resistivity at high temperature. Related mechanisms were discussed. [ABSTRACT FROM AUTHOR]

Highly (001)-oriented Cu 2- y Se thin films with tunable thermoelectric performances have been grown by pulsed laser deposition. By using targets with different Cu/Se ratios that further determines the copper deficiency of as-grown films, the carrier concentrations of as-grown films are tuned within a broad range from 10 18 to 10 21 cm −3 . The optimum performance is observed at carrier concentration ~1.58×10 20 cm −3 . The distinct properties of Cu 2- y Se thin films with nearly ideal chemical stoichiometric ratio are observed. In addition, a weak change in the electrical transport during the second-order phase transition was observed in the thin films due to the anisotropic structure of the Cu 2- y Se. [ABSTRACT FROM AUTHOR]

Short carbon fiber-reinforced p-type skutterudite CeFe 4 Sb 12 composites were fabricated by a melting-annealing process combined with spark plasma sintering, the effect of carbon fibers on the thermoelectric and mechanical properties were investigated, and the relationship between the microstructure and the mechanical properties of the composites were elucidated. The results indicate that the carbon fibers were well distributed throughout the matrix and were in intimate contact with the CeFe 4 Sb 12 grains without interlayers. Both the flexural strength and the fracture toughness of CeFe 4 Sb 12 were enhanced with the addition of the carbon fibers. Considering the tradeoff between the thermoelectric and mechanical properties, the optimal carbon fiber content was found to be 1 vol.%. The flexural strength of the composite containing 1 vol.% fiber was improved by 53%, whereas the fracture toughness and ZT value remained nearly unchanged. [ABSTRACT FROM AUTHOR]

Minute amounts of Fe/Mn are selected to be doped into CeyCo4Sb12 filled skutterudites to slightly compensate for electrons donated by the fillers. As a direct result, the Ce filling fractions are enhanced from 0.11 to 0.16. The carrier concentrations are improved by a factor of more than two times to approach the optimal values, leading to greatly improved power factors. Meanwhile, the lattice thermal conductivity is expectedly suppressed by the increased Ce fillers in the voids of skutterudites. Consequently, a maximum ZT of 1.3 at 850 K is obtained, which is comparable to that in the best single-filled skutterudites. [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: Composite glass coating was fabricated on thermoelectric (TE) skutterudite (SKD) materials by using the dispersion system of modified nano-silica aerogel and micro glass powder. The organosilane was used as the binder in the slurry-blade process and isolated pores in micrometer size are formed due to the decomposition of polymerization product derived from organosilane and nano-silica aerogel particles at high temperature. These pores can effectively decrease the thermal conductivity of coating layer. The composite glass coating shows good stability at 823K in air. However, significant microstructural changes in the coating were observed after aging at 923K, at which the isolated micro-sized pores grew to sub-millimeter pores while the continuous composite glass coating was still maintained. The glass coated skutterudite materials show good oxidation resistance, i. e. no oxides are observed even after heating at 923K in ambient air. The present glass-coating approach is expected to be applied in fabricating skutterudite-based thermoelectric devices. [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: Thermoelectric effects and related technologies have attracted a great interest due to world-wide energy harvesting. Thermoelectricity has usually been considered in the context of stable material phases. Here we report that the fluctuation of structures during the second-order phase transition in Cu2Se semiconductor breaks the conventional trends of thermoelectric transports in normal phases, leading to a critically phase-transition-enhanced thermoelectric figure of merit zT above unity at 400K, a three times larger value than for the normal phases. Dynamic structural transformations introduce intensive fluctuations and extreme complexity, which enhance carrier entropy and thus the thermopower, and strongly scatter carriers and phonons as well to make their transports behave critically. [Copyright &y& Elsevier]

Abstract: Filling two or multiple atoms into the cages of a skutterudite crystal is a successful way to enhance the thermoelectric figure of merit in n-type partially filled skutterudites. Here we use La–Yb double filling to improve the thermoelectric performance of p-type skutterudites Yb x La y Fe2.7Co1.3Sb12 (x + y = 0.85, x = 0, 0.09, 0.17, 0.25, 0.34, 0.42, 0.85). The samples are synthesized by directly melting the raw materials followed by a long time annealing process. X-ray diffraction measurement confirms the skutterudite structure of the samples. By increasing the filling fraction of Yb, the lattice thermal conductivity is gradually depressed and reaches the lowest value of 0.9 W m−1 K−1 at high temperatures. At the same time, the Seebeck coefficient decreases while the electrical conductivity increases. The maximum power factor around 27 μW cm−1 K−2 for samples Yb0.17La0.68Fe2.7Co1.3Sb12 and Yb0.25La0.60Fe2.7Co1.3Sb12 is achieved at 600 K and 700 K, respectively. Sample Yb0.25La0.60Fe2.7Co1.3Sb12 has the maximum thermoelectric figure of merit 0.99 at 700 K, which is among the highest values among p-type filled skutterudites. [Copyright &y& Elsevier]

A two-step method has been used to fabricate nano-particles of layer-structured bismuth chalcogenide compounds, including BiTe, BiSe, and BiSeTe, through a nano-scaled top-down route. In the first step, lithium (Li) atoms are intercalated between the van der Waals bonded quintuple layers of bismuth chalcogenide compounds by controllable electrochemical process inside self-designed lithium ion batteries. And in the second step, the Li intercalated bismuth chalcogenides are subsequently exposed to ethanol, in which process the intercalated Li atoms would explode like atom-scaled bombs to exfoliate original microscaled powder into nano-scaled particles with size around 10 nm. The influence of lithium intercalation speed and amount to three types of bismuth chalcogenide compounds are compared and the optimized intercalation conditions are explored. As to maintain the phase purity of the final nano-particle product, the intercalation lithium amount should be well controlled in Se contained bismuth chalcogenide compounds. Besides, compared with binary bismuth chalcogenide compound, lower lithium intercalation speed should be applied in ternary bismuth chalcogenide compound. [ABSTRACT FROM AUTHOR]

Abstract: Ab-initio calculations of the resonant modes and frequencies for a number of possible fillers in p-type RFe3CoSb12 and RFe4Sb12 were carried out. The results indicate that, although the exact values of fillers’ resonant frequencies in p-type skutterudites are somewhat different from those in n-type Co-based skutterudites, the Einstein-like resonant modes of the fillers are similar to those in n-type materials. Experimentally, several pairs of the fillers were selected and double-filled p-type skutterudite compounds RxMy Fe3CoSb12 (R, M = Ba, Ce, Nd, and Yb) were successfully synthesized. The reduction in the lattice thermal conductivity was realized by extending the range of resonant frequencies. As a result, enhanced ZT values above unity were achieved in these double-filled p-type skutterudites. [Copyright &y& Elsevier]

Abstract: A CoSb3-based thermoelectric module was fabricated using Ce0.45Co2.5Fe1.5Sb12 p-type leg and Yb0.25Co4Sb12/Yb2O3 n-type leg. Ag–Cu foil was used to construct the junction of hot side legs. With two p–n couples, the module generated a maximum output power (P max ) of 140mW and a maximum open-circuit voltage (V o ) of 210mV under the thermal condition of hot side temperature T h =810K and a temperature difference ΔT=490K. No deterioration in output power in vacuum was seen when thermal cycle of five times for the module was carried out under T h =810K and ΔT=490K with natural cooling to room temperature, which shows the module has high durability. [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]

Abstract: Two crystals of Bi2Se0.21Te2.79 doped with 0.08wt% TeI4 were grown by zone melting on the Foton-M3 spacecraft of Russia and the ground in 2007, respectively. The chemical composition, structure and thermoelectric properties of the space and ground crystals grown were evaluated by EPMA, XRD and thermoelectric measurements including Seebeck coefficient, electrical conductivity and thermal conductivity. The compositions of the space crystal grown along growth direction were more homogeneous than that of the ground crystal grown. The crystallization of space crystal grown was obviously improved. The maximum ZT value of space crystal reached 1.14 at 300K, which was higher about 29% than that of ground crystal at room temperature. These results imply that the composition homogeneity and crystallization of Bi2Se0.21Te2.79 crystal can be improved under microgravity conditions, which is helpful for enhancing thermoelectric figure of merit of Bi2Te3-base materials. [Copyright &y& Elsevier]

Polycrystalline-filled skutterudite Ba0.2(Co1− x Ir x )4Sb12 (x= 0, 0.1, 0.2) was synthesized by melting–quenching–annealing combined with a subsequent spark plasma sintering method. A solid solution of Ir was formed at the Co sites during the first annealing step (800 °C for 7days), then Ir-rich nanocrystals with the composition Ba0.2(Co0.9Ir0.1)4Sb12 precipitated during the subsequent annealing period (550 °C for 30days). This is the first time that phase segregation has been realized in this system. The correlation of the fabrication, microstructure and thermal transport properties is discussed. [Copyright &y& Elsevier]

Abstract: Ba8Ga16Ge30 clathrate crystals were grown by Czochralski method. The influence of growth condition on the composition and thermoelectric property of the obtained crystals was investigated. The lower pulling rate and higher pressure resulted in a larger Ga/Ge ratio in the grown crystals, and the elemental composition was homogeneous. The sample with a higher Ga/Ge ratio showed the larger electrical conductivity than the sample with a lower Ga/Ge ratio, but the Seebeck coefficient was not sensitive to the Ga/Ge ratio, which led to a larger power factor. The higher Ga/Ge ratio also resulted in a lower lattice thermal conductivity and as a result led to a higher ZT value, which was measured to be 0.93 at 850K and could reach 1.3 as extrapolated to 1000K. [Copyright &y& Elsevier]

Abstract: Ge-doped TiCoSb-based half-Heusler compounds, TiCoGe x Sb1−x (x =0–0.2), were prepared by arc melting and spark plasma sintering (SPS). The electrical conductivity, Seebeck coefficient and thermal conductivity were measured from room temperature to 850K. The Seebeck coefficient changed from negative to positive by Ge doping, and the electrical conductivity increased with increasing Ge content. The lattice thermal conductivity for TiCoGe x Sb1−x is considerably reduced, because the point defects induced by Ge substitution for Sb intensively scatter the thermal phonons. The mass fluctuation part Γ mass and strain field fluctuation part Γ stra were estimated, and it was found that the reduction of lattice thermal conductivity is mainly attributed to the strain field fluctuation. Ge doping improved the thermoelectric figure of merit ZT of TiCoSb and the maximum ZT value of 0.16 was obtained for TiCoGe0.15Sb0.85 sample at 850K. [Copyright &y& Elsevier]

Abstract: Sr0.29CoO2 crystals have been successfully prepared by a low temperature ion exchange from layered Na x CoO2, and it is isomorphic to its precursor Na x CoO2 with a layered triangular structure. The thermoelectric properties of Sr0.29CoO2 crystal were measured in the temperature of 2.5–773K. A transition has been exhibited in the resistivity, Seebeck coefficient and carrier concentration at approximately 75K. The resistivity, Seebeck coefficient and power factor increase with increasing temperature, and reach the values of 2.78mΩcm, 171μV/K and 7.1×10−4 Wm−1 K−2 at 773K, respectively. [Copyright &y& Elsevier]

Lithium intercalation and de-intercalation processes have been used to fabricate bulk Bi2Se0.3Te2.7with internal nanostructures. The doped Li content can be precisely controlled through this method. It provides a chance to directly optimize electrical properties when preparing nano-structured materials, leading to the optimum carrier concentration for improved thermoelectric figure of merit. [ABSTRACT FROM AUTHOR]

The fundamental understanding of the influence of molecular structure on the carrier transport properties in the field of organic thermoelectrics (OTEs) is a big challenge since the carrier transport behavior in conducting polymers reveals average properties contributed from all carrier transport channels, including those through intra-chain, inter-chain, inter-grain, and hopping between disordered localized sites. Here, combining molecular dynamics simulations and experiments, we investigated the carrier transport properties of doped highly oriented poly(3-hexylthiophene) (P3HT) films with different side-chain regioregularity. It is demonstrated that the substitution of side chains can not only take effect on the carrier transport edge, but also on the dimensionality of the transport paths and as a result, on the carrier mobility. Conductive atomic force microscopy (C-AFM) study as well as temperature-dependent measurements of the electrical conductivity clearly showed ordered local current paths in the regular side chain P3HT films, while random paths prevailed in the irregular sample. Regular side chain substitution can be activated more easily and favors one-dimensional transport along the backbone chain direction, while the irregular sample presents the three-dimensional electron hopping behavior. As a consequence, the regular side chain P3HT samples demonstrated high carrier mobility of 2.9 ± 0.3 cm2/V·s, which is more than one order of magnitude higher than that in irregular side chain P3HT films, resulting in a maximum thermoelectric (TE) power factor of 39.1 ± 2.5 μW/mK2 at room temperature. These findings would formulate design rules for organic semiconductors based on these complex systems, and especially assist in the design of high performance OTE polymers. [ABSTRACT FROM AUTHOR]

The low weighted carrier mobility has long been considered to be the key challenge for improvement of thermoelectric (TE) performance in BiTeI. The Rashba-effect-induced two-dimensional density of states in this bulk semiconductor is beneficial for thermopower enhancement, which makes it a prospective compound for TE applications. In this report, we show that intercalation of minor Cu-dopants can substantially alter the equilibria of defect reactions, selectively mediate the donor-acceptor compensation, and tune the defect concentration in the carrier conductive network. Consequently, the potential fluctuations responsible for electron scattering are reduced and the carrier mobility in BiTeI can be enhanced by a factor of two to three between 10 K and 300 K. The carrier concentration can also be optimized by tuning the Te/I composition ratio, leading to higher thermopower in this Rashba system. Cu-intercalation in BiTeI gives rise to higher power factor, slightly lower lattice thermal conductivity, and consequently improved figure of merit. Compared with pristine BiTe0.98I1.02, the TE performance in Cu0.05BiTeI reveals a 150% and 20% enhancement at 300 and 520 K, respectively. These results demonstrate that defect equilibria mediated by selective doping in complex TE and energy materials could be an effective approach to carrier mobility and performance optimization. [ABSTRACT FROM AUTHOR]