Journal article

Publication year: 2018

Pages: 429-434

Journal: Energy & Environmental Science

Volume number: 11

Issue number: 2

ISSN: 1754-5692

eISSN: 1754-5706

Open access status: Green

DOI Link: https://doi.org/10.1039/c7ee03326e

Publisher: Royal Society of Chemistry

Abstract: 
Thermally activated mobility near room temperature is a signature of detrimental scattering that limits the efficiency and figure-of-merit zT in thermoelectric semiconductors. This effect has been observed dramatically in Mg3Sb2-based compounds, but also to a lesser extent in other thermoelectric compounds. Processing samples differently or adding impurities such that this effect is less noticeable produces materials with a higher zT. Experiments suggest that the behavior is related to grain boundaries, but impurity scattering has also been proposed. However, conventional models using Matthissen's rule are not able to explain the dramatic change in the temperature dependency of conductivity or drift mobility which is observed in Mg3Sb2-based compounds. We find that it is essential to consider the grain boundary region as an effectively separate phase rather than a scattering center, taking into account the weaker screening in semiconductors compared with classical metals. By modeling a grain boundary phase with a band offset, we successfully reproduce the experimentally observed conductivity versus temperature and thermopower versus conductivity relations, which indicate an improved description of transport. The model shows good agreement with measured grain size dependencies of conductivity, opening up avenues for quantitatively engineering materials with similar behavior. Model estimates predict room for 460% improvement in the room temperature zT of Mg3.2Sb1.5Bi0.49Te0.01 if the grain boundary resistance could be eliminated.

Harvard Citation style: Kuo, J., Kang, S., Imasato, K., Tamaki, H., Ohno, S., Kanno, T., et al. (2018) Grain boundary dominated charge transport in Mg₃Sb₂-based compounds, Energy & Environmental Science, 11(2), pp. 429-434. https://doi.org/10.1039/c7ee03326e

APA Citation style: Kuo, J., Kang, S., Imasato, K., Tamaki, H., Ohno, S., Kanno, T., & Snyder, G. (2018). Grain boundary dominated charge transport in Mg₃Sb₂-based compounds. Energy & Environmental Science. 11(2), 429-434. https://doi.org/10.1039/c7ee03326e