skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Using the 18-Electron Rule To Understand the Nominal 19-Electron Half-Heusler NbCoSb with Nb Vacancies

Authors:
ORCiD logo [1];  [2];  [3];  [4];  [4]; ORCiD logo [4]; ORCiD logo [2];  [2]
  1. Physikalisch-Chemisches Institut, Justus-Liebig-Universität Giessen, Heinrich-Buff-Ring 17, 35392 Giessen, Germany
  2. Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, United States
  3. Center for Advanced Materials and Energy, Xihua University, Chengdu, Sichuan 610039, China
  4. Department of Physics and TcSUH, University of Houston, Houston, Texas 77204, United States
Publication Date:
Research Org.:
Energy Frontier Research Centers (EFRC) (United States). Solid-State Solar-Thermal Energy Conversion Center (S3TEC)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1388395
DOE Contract Number:
SC0001299; FG02-09ER46577
Resource Type:
Journal Article
Resource Relation:
Journal Name: Chemistry of Materials; Journal Volume: 29; Journal Issue: 3; Related Information: S3TEC partners with Massachusetts Institute of Technology (lead); Boston College; Oak Ridge National Laboratory; Rensselaer Polytechnic Institute
Country of Publication:
United States
Language:
English
Subject:
solar (photovoltaic), solar (thermal), solid state lighting, phonons, thermal conductivity, thermoelectric, defects, mechanical behavior, charge transport, spin dynamics, materials and chemistry by design, optics, synthesis (novel materials), synthesis (self-assembly), synthesis (scalable processing)

Citation Formats

Zeier, Wolfgang G., Anand, Shashwat, Huang, Lihong, He, Ran, Zhang, Hao, Ren, Zhifeng, Wolverton, Chris, and Snyder, G. Jeffrey. Using the 18-Electron Rule To Understand the Nominal 19-Electron Half-Heusler NbCoSb with Nb Vacancies. United States: N. p., 2017. Web. doi:10.1021/acs.chemmater.6b04583.
Zeier, Wolfgang G., Anand, Shashwat, Huang, Lihong, He, Ran, Zhang, Hao, Ren, Zhifeng, Wolverton, Chris, & Snyder, G. Jeffrey. Using the 18-Electron Rule To Understand the Nominal 19-Electron Half-Heusler NbCoSb with Nb Vacancies. United States. doi:10.1021/acs.chemmater.6b04583.
Zeier, Wolfgang G., Anand, Shashwat, Huang, Lihong, He, Ran, Zhang, Hao, Ren, Zhifeng, Wolverton, Chris, and Snyder, G. Jeffrey. Wed . "Using the 18-Electron Rule To Understand the Nominal 19-Electron Half-Heusler NbCoSb with Nb Vacancies". United States. doi:10.1021/acs.chemmater.6b04583.
@article{osti_1388395,
title = {Using the 18-Electron Rule To Understand the Nominal 19-Electron Half-Heusler NbCoSb with Nb Vacancies},
author = {Zeier, Wolfgang G. and Anand, Shashwat and Huang, Lihong and He, Ran and Zhang, Hao and Ren, Zhifeng and Wolverton, Chris and Snyder, G. Jeffrey},
abstractNote = {},
doi = {10.1021/acs.chemmater.6b04583},
journal = {Chemistry of Materials},
number = 3,
volume = 29,
place = {United States},
year = {Wed Jan 25 00:00:00 EST 2017},
month = {Wed Jan 25 00:00:00 EST 2017}
}
  • The 18-electron rule is a widely used criterion in the search for new half-Heusler thermoelectric materials. However, several 19-electron compounds such as NbCoSb have been found to be stable and exhibit thermoelectric properties rivaling state-of-the art materials. Using synchrotron X-ray diffraction and density functional theory calculations, we show that samples with nominal (19-electron) composition NbCoSb actually contain a half-Heusler phase with composition Nb0.84CoSb. The large amount of stable Nb vacancies reduces the overall electron count, which brings the stoichiometry of the compound close to an 18-electron count, and stabilizes the material. Excess electrons beyond 18 electrons provide heavy doping neededmore » to make these good thermoelectric materials. This work demonstrates that considering possible defect chemistry and allowing small variation of electron counting leads to extra degrees of freedom for tailoring thermoelectric properties and exploring new compounds. Here we discuss the 18-electron rule as a guide to find defect-free half-Heusler semiconductors. Other electron counts such as 19-electron NbCoSb can also be expected to be stable as n-type metals, perhaps with cation vacancy defects to reduce the electron count.« less
  • Highlights: • Half-Heusler alloy NbCoSb with 19 valence electron count was studied as TE material. • It is surprising that NbCoSb is n-type. • A maximum ZT of ∼0.4 is achieved at 700 °C without optimization. • It opens up a new route to develop new half-Heusler thermoelectric materials. • It is very interesting that a traditionally thought of VEC of 18 is not required. - Abstract: We surprisingly made a new n-type thermoelectric compound NbCoSb with half-Heusler (HH) structure having valence electron count of 19, different from the traditional 18, which opens up a new route to develop newmore » half-Heusler thermoelectric materials not following the traditional valence electron count of 18. The samples are made by arc melting followed by ball milling and hot pressing. The effect of hot pressing temperature on the thermoelectric properties of NbCoSb samples has been studied. A maximum thermoelectric figure-of-merit (ZT) of ∼0.4 is achieved at 700 °C in NbCoSb sample that is hot pressed at 1000 °C. This work add a new member to HH compounds for thermoelectric applications, although the peak ZT of ∼0.4 is still lower than that of the traditional HHs. Moreover, it is very interesting to see that a traditionally thought of valence electron counts of 18 is not required.« less