Metal distributions, efficient n-type doping, and evidence for in-gap states in TiNiMySn (M = Co, Ni, Cu) half-Heusler nanocomposites

Downie, R. A., Smith, R. I., MacLaren, D. A. and Bos, J.-W. G. (2015) Metal distributions, efficient n-type doping, and evidence for in-gap states in TiNiMySn (M = Co, Ni, Cu) half-Heusler nanocomposites. Chemistry of Materials, 27(7), pp. 2449-2459. (doi:10.1021/cm5045682)

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Publisher's URL: http://dx.doi.org/10.1021/cm5045682

Abstract

XNi1+ySn nanocomposites consisting of a XNiSn half-Heusler (HH) matrix with segregated XNi2Sn Full Heusler (FH) inclusions promise improvements in thermoelectric efficiencies. We extend recent research by reporting on TiNiMySn (0 ≤ y ≤ 1) nanocomposites with M = Co (3d9), Ni (3d10) and Cu (3d104s1). Neutron powder diffraction reveals that the Ni and Cu series produce a matrix of TiNiSn with nanosegregated TiNi2Sn and TiNi1+dCu1–dSn, respectively. For the Co series, the Co inserts into both phases to obtain a TiNi1–yCoySn matrix with nanosegregated TiNi2–yCoySn. Systematic changes in Seebeck coefficient (S) and electrical resistivity (ρ) are observed in all three series. For M = Ni, changes in S and ρ are attributed to in-gap states arising from the nanosegregation. The M = Co composites show a complex interplay between the hole doped TiNi1–yCoySn matrix and similar in-gap states, where the p- to n-type transition temperature increases but the maximum S remains unchanged at +30 μV K–1. The 4s1 electron for M = Cu is delocalized in the HH matrix, leading to metal-like ρ(T) and up to 100% improved thermoelectric power factors compared to TiNiSn (S2/ρ = 2 mW m–1 K–2 at 600–700 K for y = 0.025). These results broaden the range of segregated FH phases that could be used to enhance HH thermoelectric performance.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:MacLaren, Dr Donald
Authors: Downie, R. A., Smith, R. I., MacLaren, D. A., and Bos, J.-W. G.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Chemistry of Materials
Publisher:American Chemical Society
ISSN:0897-4756
ISSN (Online):1520-5002
Copyright Holders:Copyright © 2015 American Chemical Society
First Published:First published in Chemistry of Materials 27(7):2449-2459
Publisher Policy:Reproduced under a Creative Commons License

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