Search

The band structure of PbTe can be manipulated by alloying with MgTe to control the band degeneracy. This is used to stabilize the optimal carrier concentration, making it less temperature dependent, demonstrating a new strategy to improve overall thermoelectric efficiency over a broad temperature range., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Ge-Sb-Te compounds (GST), the well-known phase-change materials, are considered to be promising thermoelectric (TE) materials due to their decent thermoelectric performance. While Ge2Sb2Te5 and GeSb2Te4 have been extensively studied, the TE performance of GeSb4Te7 has not been well explored. Reducing the excessive carrier concentration is crucial to improving TE performance for GeSb4Te7. In this work, we synthesize a series of Se-alloyed GeSb4Te7 compounds and systematically investigate their structures and transport properties. Raman analysis reveals that Se alloying introduces a new vibrational mode of GeSe2, enhancing the interatomic interaction forces within the layers and leading to the reduction of carrier concentration. Additionally, Se alloying also increases the effective mass and thus improves the Seebeck coefficient of GeSb4Te7. The decrease in carrier concentration reduces the carrier thermal conductivity, depressing the total thermal conductivity. Finally, a maximum zT value of 0.77 and an average zT value of 0.48 (300–750 K) have been obtained in GeSb4Te5.5Se1.5. This work investigates the Raman vibration modes and the TE performance in Se-alloyed GeSb4Te7 sheddinglight on the performance optimization of other GST materials. [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]

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]