A simple model for vacancy order and disorder in defective half-Heusler systems

IUCrJ
Nikolaj RothBo B Iversen

Abstract

Defective half-Heusler systems X1-xYZ with large amounts of intrinsic vacancies, such as Nb1-x CoSb, Ti1-x NiSb and V1-x CoSb, are a group of promising thermoelectric materials. Even with high vacancy concentrations they maintain the average half-Heusler crystal structure. These systems show high electrical conductivity but low thermal conductivity arising from an ordered YZ substructure, which conducts electrons, while the large amounts of vacancies in the X substructure effectively scatters phonons. Using electron scattering, it was recently observed that, in addition to Bragg diffraction from the average cubic half-Heusler structure, some of these samples show broad diffuse scattering indicating short-range vacancy order, while other samples show sharp additional peaks indicating long-range vacancy ordering. Here it is shown that both the short- and long-range ordering can be explained using the same simple model, which assumes that vacancies in the X substructure avoid each other. The samples showing long-range vacancy order are in agreement with the predicted ground state of the model, while short-range order samples are quenched high-temperature states of the system. A previous study showed that changes in sample stoichio...Continue Reading

References

Jan 26, 2008·Nature Materials·G Jeffrey Snyder, Eric S Toberer
May 21, 2010·Acta Crystallographica. Section B, Structural Science·R L WithersD Orobengoa
Dec 29, 2010·Nano Letters·Xiao YanZ F Ren
Mar 13, 2012·Nature Materials·Huili LiuG Jeffrey Snyder
May 23, 2015·Nature·David A Keen, Andrew L Goodwin
Feb 5, 2016·Nature Communications·Alistair R OveryAndrew L Goodwin
Mar 7, 2017·Advanced Materials·Tiejun ZhuXinbing Zhao
Dec 24, 2018·Acta Crystallographica. Section A, Foundations and Advances·Joseph A M Paddison
May 2, 2019·Acta Crystallographica. Section A, Foundations and Advances·Nikolaj Roth, Bo B Iversen

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Citations

Apr 13, 2021·Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials·Dorota A KowalskaMarek Wołcyrz
Jun 18, 2021·Chemical Society Reviews·Yun ZhengMercouri G Kanatzidis
Jul 15, 2021·IUCrJ·Nikolaj RothBo B Iversen

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Methods Mentioned

BETA
X-ray
electron scattering
electron diffraction
thermal treatment
electron-diffraction

Software Mentioned

custom
Python
Scatty

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