Thermoelectric Transport Properties of n-Type Sb-doped (Hf,Zr,Ti)NiSn Half-Heusler Alloys Prepared by Temperature-Regulated Melt Spinning and Spark Plasma Sintering

Ki Wook Bae,Jeong Yun Hwang,Sang-Il Kim,Kyu Hyoung Lee,Hyung Mo Jeong,Sunuk Kim,Hyun-Sik Kim,Jae-Hong Lim

doi:10.3390/app10144963

Abstract

Herein we report a significantly reduced lattice thermal conductivity of Sb-doped Hf0.35Zr0.35Ti0.3NiSn half-Heusler alloys with sub-micron grains (grain size of ~300 nm). Polycrystalline bulks of Hf0.35Zr0.35Ti0.3NiSn1−xSbx (x = 0.01, 0.02, 0.03) with a complete single half-Heusler phase are prepared using temperature-regulated melt spinning and subsequent spark plasma sintering without a long annealing process. In these submicron-grained bulks, a very low lattice thermal conductivity value of ~2.4 W m−1 K−1 is obtained at 300 K due to the intensified phonon scatterings by highly dense grain boundaries and point-defects (Zr and Ti substituted at Hf-sites). A maximum thermoelectric figure of merit, zT, of 0.5 at 800 K is obtained in Hf0.35Zr0.35Ti0.3NiSn0.99Sb0.01.

Highlights

Thermoelectric power generation (TEG) is one of the most important energy harvesting technologies that can directly generate electricity from waste heat
The requirement of a long annealing time to acquire a single-phase of a half-Heusler compound is another issue, as a conventional melt-solidification process produces full-Heusler and M-Sn binary alloys in addition to the half-Heusler phase [12]
A complete single-phase of Sb-doped (Hf,Zr,Ti)NiSn was obtained without a long annealing time, and a zT of 0.5 at 800 K was obtained in (Hf0.5 Zr0.5 )0.7 Ti0.3 NiSn0.99 Sb0.01 which benefited from a reduced κlat due to the intensified boundary phonon scattering

Summary

Introduction

Thermoelectric power generation (TEG) is one of the most important energy harvesting technologies that can directly generate electricity from waste heat. For commercialization of ATEGs, a few material systems, including PbTe-, skutterudite-, and half-Heusler-based compounds, have been studied to develop economically feasible high-performance TE materials [1,2,3]. Considering the severe thermo-mechanical stresses that a TEG system under operation are exposed to, high thermal stability [6] and mechanical reliability [7] of half-Heusler-based compounds make them a strong candidate material for TEG systems. Their zTs are relatively lower than those of other material systems for mid-to-high temperature applications, including PbTe- and skutterudite-based compounds, owing to their high κ [4]. A complete single-phase of Sb-doped (Hf,Zr,Ti)NiSn was obtained without a long annealing time, and a zT of 0.5 at 800 K was obtained in (Hf0.5 Zr0.5 )0.7 Ti0.3 NiSn0.99 Sb0.01 which benefited from a reduced κlat due to the intensified boundary phonon scattering

Materials and Methods

Results and Discussion

Conclusions