Open AccessThermal properties of TiNiSn and VFeSb half-Heusler thermoelectrics from synchrotron x-ray powder diffraction
Author(s) -
Daniella A. Ferluccio,
Blair Fitzgerald Kennedy,
Sonia A. Barczak,
Srinivasa R. Popuri,
Claire Murray,
M. Pollet,
JanWillem G. Bos
Publication year - 2021
Publication title -
jphys energy
Language(s) - English
Resource type - Journals
ISSN - 2515-7655
DOI - 10.1088/2515-7655/abf41a
Subject(s) - materials science , synchrotron , thermal expansion , thermoelectric materials , diffraction , lattice constant , x ray crystallography , condensed matter physics , thermoelectric effect , debye model , intermetallic , crystallography , thermodynamics , thermal conductivity , metallurgy , composite material , optics , chemistry , physics , alloy
Half-Heusler (HH) alloys are an important class of thermoelectric materials that combine promising performance with good engineering properties. This manuscript reports a variable temperature synchrotron x-ray diffraction study of several TiNiSn- and VFeSb-based HH alloys. A Debye model was found to capture the main trends in thermal expansion and atomic displacement parameters. The linear thermal expansion coefficient α(T) of the TiNiSn-based samples was found to be independent of alloying or presence of Cu interstitials with α av = 10.1 × 10 −6 K −1 between 400 and 848 K. The α(T) of VFeSb and TiNiSn are well-matched, but NbFeSb has a reduced α av = 8.9 × 10 −6 K −1 , caused by a stiffer lattice structure. This is confirmed by analysis of the Debye temperatures, which indicate significantly larger bond force constants for all atomic sites in NbFeSb. This work also reveals substantial amounts of Fe interstitials in VFeSb, whilst these are absent for NbFeSb. The Fe interstitials are linked to low thermal conductivities, but also reduce the bandgap and lower the onset of thermal bipolar transport.