Using phase boundary mapping to resolve discrepancies in the Mg2Si-Mg2Sn miscibility gap

Rachel Orenstein, James P. Male, Michael Toriyama, Shashwat Anand, G. Jeffrey Snyder*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Mg2Si-Mg2Sn compositions within the Mg-Si-Sn materials system have potential as inexpensive, efficient thermoelectrics. These compositions lie specifically along the pseudobinary line with compositions of Mg2Si1−xSnx. The alloying and possible nanostructuring within the miscibility gap could further increase the thermoelectric figure of merit (zT) for these materials. However, the solubility limits of the miscibility gap differ greatly in the literature. Such a discrepancy could be a result of differing Mg-compositions due to excess magnesium added during sample annealing. To define these limits better and explain the change in proposed solubility limits based on magnesium content, the three-phase regions on either side of the pseudobinary phase region are phase boundary mapped and defect energy calculations are performed. This study presents a new understanding of the Mg-Si-Sn ternary phase diagram around the pseudobinary phase region. The solubility limits on either side of the pseudobinary should be essentially identical between the Mg-rich and Mg-poor three-phase regions unless the system temperature is brought above about 565 °C, at which eutectic liquid Mg0.9Sn0.1forms. This creates a second Mg-rich three-phase region which intersects the pseudobinary with a lower Sn solubility. Thus, samples prepared along the pseudobinary line are not well-defined thermodynamically when excess magnesium is added. Excess Mg can push the system into a new three phase region with Mg2Si1−xSnxcomposition different from that of the true miscibility gap. This understanding presents new guidelines for evaluating the miscibility gap and assists strategies for microstructure engineering and thermoelectric material processing.

Original languageEnglish (US)
Pages (from-to)7208-7215
Number of pages8
JournalJournal of Materials Chemistry A
Volume9
Issue number11
DOIs
StatePublished - Mar 21 2021

ASJC Scopus subject areas

  • Chemistry(all)
  • Renewable Energy, Sustainability and the Environment
  • Materials Science(all)

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