A strategy to optimize the thermoelectric performance in a spark plasma sintering process.

Wan-Ting Chiu,Yang-Yuan Chen,Cheng-Lung Chen

doi:10.1038/srep23143

Abstract

Spark plasma sintering (SPS) is currently widely applied to existing alloys as a means of further enhancing the alloys’ figure of merit. However, the determination of the optimal sintering condition is challenging in the SPS process. This report demonstrates a systematic way to independently optimize the Seebeck coefficient S and the ratio of electrical to thermal conductivity (σ/κ) and thus achieve the maximum figure of merit zT = S2(σ/κ)T. Sb2−xInxTe3 (x = 0–0.2) were chosen as examples to validate the method. Although high sintering temperature and pressure are helpful in enhancing the compactness and electrical conductivity of pressed samples, the resultant deteriorated Seebeck coefficient and increasing thermal conductivity eventually offset the benefit. We found that the optimal sintering temperature coincides with temperatures at which the maximum Seebeck coefficient begins to degrade, whereas the optimal sintering pressure coincided with the pressure at which the σ/κ ratio reaches a maximum. Based on this principle, the optimized sintering conditions were determined, and the zT of Sb1.9In0.1Te3 is raised to 0.92 at 600 K, showing an approximately 84% enhancement. This work develops a facile strategy for selecting the optimal SPS sintering condition to further enhance the zT of bulk specimens.

Highlights

Seebeck coefficient begins to degrade, proving the effectiveness of this strategy in the zT enhancement of bulk Sb2−xInxTe3 (x = 0–0.2) alloys
We examined the applicability of our approach to other thermoelectric material systems and confirmed its generalisability to other systems that can be densified by the SPS process
The result is consistent with that reported by Rosenberg et al.[23,24,25] and suggests that the added indium can successfully fill into the Sb site

Summary

Introduction

Because Sb-Te bond has relatively lower bond polarity compared with Bi-Te, the antisite defects are more severe in Sb-Te. More defects in the lattice certainly contribute extra carriers, too many of which inevitably lead to a poorer Seebeck coefficient and higher thermal conductivity[15]. Doping effects on Sb2Te3 have been intensively studied for theoretical and applicational purposes. Dopant candidates such as bismuth[16], selenium[17], titanium[18], vanadium[19], and indium[20,21] have been examined. Under optimal SPS conditions, the In-doped Sb2Te3 alloys exhibited good thermoelectric performance with a zT value of approximately 0.73 at 600 K22. The optimal SPS criterion was applied to all other specimens to validate the methodology in engineering thermoelectric materials

Methods

Results

Conclusion