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)

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, Professor 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