High-ZT half-Heusler thermoelectrics, Ti0.5Zr0.5NiSn and Ti0.5Zr0.5NiSn0.98Sb0.02: Physical properties at low temperatures

Author(s)
G. Rogl, K. Yubuta, V. V. Romaka, H. Michor, E. Schafler, A. Grytsiv, E. Bauer, P. Rogl
Abstract

With a small gap in the density of states and a substantially semiconducting behavior half Heusler alloys have drawn attention as thermoelectric materials. For this study we have selected Hf-free compounds, Ti0.5Zr0.5NiSn, Ti0.5Zr0.5NiSn (with a densification aid (DA)) and Ti0.5Zr0.5NiSn0.98Sb0.02 as well their parent alloys TiNiSn and ZrNiSn as cheap thermoelectrics. Electrical resistivity, thermal conductivity and specific heat were evaluated below room temperature (4.2-300 K) in order to get insight into the mechanism of transport properties. SEM and TEM investigations as well as DFT (density functional theory) calculations accompany this research. The fine-grained epitaxial microstructure with a large number of dislocations warrants a low thermal conductivity at ultralow values (similar to 30 mW/cmK at 300 K) at a narrow band gap with a sufficiently high density of states at the Femi level. High order of components mixing strongly affects the stability of the solid solutions by the configuration entropy term, which causes a shrinkage of the miscibility gap. For the electronic density of states (DOS) the split Zr band and impurity Ni band induce a significant reduction of the effective energy gap and thus explain n-type of conductivity of the compounds and solid solutions studied. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Organisation(s)
Department of Materials Chemistry, Physics of Nanostructured Materials
External organisation(s)
Tohoku University, Lviv Polytechnic National University, Leibnitz Inst Solid State & Mat Res, Leibniz Institute for Solid State & Materials Research Dresden, Christian Doppler Laboratory for Thermoelectricity, Technische Universität Wien
Journal
Acta Materialia
Volume
166
Pages
466-483
No. of pages
18
ISSN
1359-6454
DOI
https://doi.org/10.1016/j.actamat.2018.12.042
Publication date
03-2019
Peer reviewed
Yes
Austrian Fields of Science 2012
Physical chemistry, Materials chemistry
Keywords
Portal url
https://ucris.univie.ac.at/portal/en/publications/highzt-halfheusler-thermoelectrics-ti05zr05nisn-and-ti05zr05nisn098sb002-physical-properties-at-low-temperatures(e44d0287-f1b7-4b3c-bf31-7b2df3d22c8c).html