Achieving zT > 1 in Inexpensive Zintl Phase Ca9Zn4+ xSb9 by Phase Boundary Mapping

Saneyuki Ohno, Umut Aydemir, Maximilian Amsler, Jan Hendrik Pöhls, Sevan Chanakian, Alex Zevalkink, Mary Anne White, Sabah K. Bux, Chris Wolverton, G. Jeffrey Snyder*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

139 Scopus citations

Abstract

Complex multinary compounds (ternary, quaternary, and higher) offer countless opportunities for discovering new semiconductors for applications such as photovoltaics and thermoelectrics. However, controlling doping has been a major challenge in complex semiconductors as there are many possibilities for charged intrinsic defects (e.g., vacancies, interstitials, antisite defects) whose energy depends on competing impurity phases. Even in compounds with no apparent deviation from a stoichiometric nominal composition, such defects commonly lead to free carrier concentrations in excess of 1020 cm−3. Nevertheless, by slightly altering the nominal composition, these defect concentrations can be tuned with small variation of the chemical potentials (composition) of each element. While the variation of chemical composition is undetectable, it is shown that the changes can be inferred by mapping (in nominal composition space) the boundaries where different competing impurity phases form. In the inexpensive Zintl compound Ca9Zn4+ xSb9, the carrier concentrations can be finely tuned within three different three-phase regions by altering the nominal composition (x = 0.2–0.8), enabling the doubling of thermoelectric performance (zT). Because of the low thermal conductivity, the zT can reach as high as 1.1 at 875 K, which is one of the highest among the earth abundant p-type thermoelectrics with no ion conducting.

Original languageEnglish (US)
Article number1606361
JournalAdvanced Functional Materials
Volume27
Issue number20
DOIs
StatePublished - May 25 2017

Funding

This work was supported by the NASA Science Mission Directorate's Radioisotope Power Systems Thermoelectric Technology Development. S.O. acknowledges the financial assistance of Japan Student Service Organization (JASSO) and would like to thank Stephen Dongmin Kang and Max Wood for the helpful discussions. M.A.W. acknowledges the support of NSERC and the Materials Characterization Facilities at Dalhousie University's Institute for Research in Materials. J.-H.P. is grateful to the NSERC CREATE DREAMS (Dalhousie Research in Energy, Advanced Materials and Sustainability program) for funding. M.A. acknowledges the support from the Novartis Universität Basel Excellence Scholarship for Life Sciences and the Swiss National Science Foundation (Grant No. P300P2-158407). C.W. (DFT calculations) acknowledges the support from the DOE (Grant No. DE-FG02-07ER46433). The Swiss National Supercomputing Center in Lugano (Project s499, s621, and s700), the Extreme Science and Engineering Discovery Environment (XSEDE) (which was supported by the National Science Foundation Grant No. OCI-1053575), the Bridges system at the Pittsburgh Supercomputing Center (PSC) (which was supported by the NSF Award No. ACI-1445606), and the National Energy Research Scientific Computing Center (DOE: DE-AC02-05CH11231), are gratefully acknowledged.

Keywords

  • Zintl phases
  • energy conversion
  • phase boundary mapping
  • semiconductors
  • thermoelectrics

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • General Chemistry
  • Condensed Matter Physics
  • General Materials Science
  • Electrochemistry
  • Biomaterials

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