Improvement of Low-Temperature zT in a Mg3Sb2–Mg3Bi2 Solid Solution via Mg-Vapor Annealing

Maxwell Wood, Jimmy Jiahong Kuo, Kazuki Imasato, Gerald Jeffrey Snyder*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

31 Scopus citations

Abstract

Materials with high zT over a wide temperature range are essential for thermoelectric applications. n-Type Mg3Sb2-based compounds have been shown to achieve high zT at 700 K, but their performance at low temperatures (<500 K) is compromised due to their highly resistive grain boundaries. Syntheses and optimization processes to mitigate this grain-boundary effect has been limited due to loss of Mg, which hinders a sample's n-type dopability. A Mg-vapor anneal processing step that grows a sample's grain size and preserves its n-type carrier concentration during annealing is demonstrated. The electrical conductivity and mobility of the samples with large grain size follows a phonon-scattering-dominated T−3/2 trend over a large temperature range, further supporting the conclusion that the temperature-activated mobility in Mg3Sb2-based materials is caused by resistive grain boundaries. The measured Hall mobility of electrons reaches 170 cm2 V−1 s−1 in annealed 800 °C sintered Mg3 + δSb1.49Bi0.5Te0.01, the highest ever reported for Mg3Sb2-based thermoelectric materials. In particular, a sample with grain size >30 mm has a zT 0.8 at 300 K, which is comparable to commercial thermoelectric materials used at room temperature (n-type Bi2Te3) while reaching zT 1.4 at 700 K, allowing applications over a wider temperature scale.

Original languageEnglish (US)
Article number1902337
JournalAdvanced Materials
Volume31
Issue number35
DOIs
StatePublished - Aug 2019

Keywords

  • MgSb
  • grain boundaries
  • ionized impurities
  • thermoelectrics
  • vapor annealing

ASJC Scopus subject areas

  • Materials Science(all)
  • Mechanics of Materials
  • Mechanical Engineering

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