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Published December 7, 2016 | Published
Journal Article Open

Thermal stability of Mg_2Si_(0.4)Sn_(0.6) in inert gases and atomic-layer-deposited Al_2O_3 thin film as a protective coating


Mg_2Si_(1−x)Sn_x solid solutions are promising thermoelectric materials to be applied in vehicle waste-heat recovery. Their thermal stability issue, however, needs to be addressed before the materials can be applied in practical thermoelectric devices. In this work, we studied the crystal structure and chemical composition of Mg_2Si_(1−x)Sn_x in inert gas atmosphere up to 823 K. We found that the sample was oxidized even in high-purity inert gases. Although no obvious structural change has been found in the slightly oxidized sample, carrier concentration decreased significantly since oxidation creates Mg vacancies in the lattice. We demonstrated that an atomic-layer deposited Al_2O_3 coating can effectively protect Mg_2Si_(1−x)Sn_x from oxidation in inert gases and even in air. In addition, this Al_2O_3 thin film also provides in situ protection to the Sb-doped Mg_2Si_(1−x)Sn_x samples during the laser-flash measurement and therefore eliminates the measurement error that occurs in uncoated samples as a result of sample oxidation and graphite exfoliation issues.

Additional Information

© 2016 The Royal Society of Chemistry. Received 02 Sep 2016, Accepted 20 Oct 2016, First published online 21 Oct 2016. This work was supported by the National Science Foundation (NSF)-Department of Energy (DOE) Joint Thermoelectric Partnership (NSF Award No. CBET1048767). The SPS equipment used for materials consolidation was acquired with the support of a NSF Major Research Instrumentation (MRI) award (DMR-1229131). The PPMS instrument for thermoelectric measurements was acquired with the support of the NSF Materials Interdisciplinary Research Team (MIRT) award (DMR1122603). The scanning Seebeck measurements were acquired with the support of Solid-State Solar-Thermal Energy Conversion Center (S3TEC), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award No. DE-SC0001299.

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