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Poly(3-hexylthiophene) (P3HT) films were prepared by using raw P3HT powders with different molecular configurations through solution processing and doped with ferric salt of triflimide anions [Fe(TFSI)], and their thermoelectric (TE) properties were studied. It was found that P3HT with highly regular molecular configuration formed highly ordered chain arrangements in P3HT film (denoted rr-P3HT film), while P3HT with irregular molecular configuration formed random chain arrangements in P3HT film (denoted ra-P3HT film). The ordered chain arrangement in rr-P3HT not only improved the charge carrier mobility but also contributed to produce more carriers, thereby remarkably improving the electrical conductivity. The electrical conductivity of rr-P3HT film was up to 96.1 S/cm, more than two orders of magnitude higher than that of ra-P3HT film. Consequently, the power factor of rr-P3HT film reached 17.10 μW/(m K), about one order of magnitude higher than that of ra-P3HT film and among the best values for pure P3HT TE materials. This study suggests that P3HT with highly regular configuration contributes to form highly ordered molecular chain arrangements, resulting in improved TE properties. [ABSTRACT FROM AUTHOR]

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]

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: 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: 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]