Abstract
Functionally graded thermoelectric materials (FGTMs) have been prepared by sedimentation of atoms under a strong gravitational field. Starting samples of BixSb1−x alloys with different composition x were synthesized by melting of metals and subsequent annealing of quenched samples. The thermoelectric properties (Seebeck coefficient, electrical conductivity) of the starting materials were characterized over the temperature range from 300 K to 525 K. Strong gravity experiments were performed in a unique ultracentrifuge apparatus under acceleration of over 0.5 × 106 G at temperatures of 538 K and 623 K. Changes of the microstructure and chemical composition were analyzed using scanning electron microscopy with energy-dispersive x-ray spectroscopy analysis. The distribution of the Seebeck coefficient of the Bi-Sb alloys was characterized by scanning thermoelectric microprobe. As a result of sedimentation, large changes in chemical composition (x = 0.45 to 1) were obtained. It was found that the changes in chemical composition were correlated with alterations of the Seebeck coefficient. The obtained experimental data allowed the development of a semiempirical model for the selection of optimal processing parameters for preparation of Bi-Sb alloys with required thermoelectric properties.
Highlights
Thermoelectric materials are currently being considered for construction of innovative devices for waste heat recovery and cooling purposes
One of the typical approaches used to overcome this problem is preparation of inhomogeneous elements by joining of a few segments made of different alloys (e.g., Bi2Te3, CoSb3) with thermoelectric properties carefully selected for the temperatures present in the thermoelectric element (TE) element
The power factor a2r of each sample reached a maximum at about 323 K (4.0 9 10À3 for sample D). These results for the thermoelectric properties are in good agreement with those reported in literature for 300 K (Table II)
Summary
Thermoelectric materials are currently being considered for construction of innovative devices for waste heat recovery and cooling purposes. Their advantages include reliability and no need for maintenance, but there is still a need for research on efficiency improvement of such materials. One of the typical approaches used to overcome this problem is preparation of inhomogeneous elements by joining of a few segments made of different alloys (e.g., Bi2Te3, CoSb3) with thermoelectric properties carefully selected for the temperatures present in the TE element.
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