Thermoelectric Properties of Bi-Doped Magnesium Silicide Stannides.

Author(s) Macario, L.Roberta; Cheng, X.; Ramirez, D.; Mori, T.; Kleinke, H.
Journal ACS Appl Mater Interfaces
Date Published 2018 Nov 02

Mg2(Si,Sn)-based compounds have shown great promise for thermoelectric applications, as they are non-toxic and comprised of abundantly available constituent elements. In this work, the crystal structures and thermoelectric properties of polycrystalline materials with nominal compositions Mg2Si0.35Sn0.65-xBix (x = 0, 0.015, 0.030, and 0.045) and Mg2SiySn0.97-yBi0.03 (y = 0.30, 0.325, and 0.35) have been investigated. The electrical conductivity, Seebeck coefficient, and thermal conductivity are strongly affected by the presence of Bi. Undoped samples showed lower values of Seebeck coefficients (below 600 K), electrical conductivity, and thermal conductivity (above 600 K) in comparison to the Bi-doped samples. Furthermore, the signs of Seebeck coefficients are all negative, confirming that n-type conduction is dominant in these materials. Electrical conductivity was enhanced by increasing of the Bi content up to 3% on the Si/Sn site due to the increasing amount of electron donors, and the absolute value of Seebeck coefficient decreased. When the Bi content is greater than 3%, lower zT values were obtained at 773 K. Thermal conductivity values might decrease with increasing Sn alloying for Mg2SiySn0.97-yBi0.03, since mass and strain fluctuation caused by alloying can effectively scatter phonons. However, a different behaviour was observed in higher Sn content material, possibly due to the absence of Mg atoms at the interstitial site (Mgi, on (½, ½, ½)) and vacancies of Mg atoms at the (¼, ¼, ¼) site, as confirmed by Rietveld refinements. Outstanding figure of merit values in excess of unity were achieved with all samples, culminating in zTmax = 1.35.

DOI 10.1021/acsami.8b15111
ISSN 1944-8252
Citation Macario LR, Cheng X, Ramirez D, Mori T, Kleinke H. Thermoelectric Properties of Bi-Doped Magnesium Silicide Stannides. ACS Appl Mater Interfaces. 2018.

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