The Effect of Crystal Mismatch on the Thermoelectric Performance Enhancement of Nano Cu2Se

Yunus Demirci,Bejan Hamawandi,Muhammet S Toprak,Aminu Yusuf,Sedat Ballikaya

doi:10.3389/fmats.2020.581138

Abstract

In the past decades, Cu2−xSe compounds have attracted great attention due to the inclusion of non-toxic and abundant elements, besides having a promising thermoelectric (TE) performance. In this work, we investigated the effect of a crystal mismatch of a nanoinclusion phase on the TE properties of Cu2−xSe. Nano-Cu2Se was synthesized using microwave assisted thermolysis, while the p-type skutterudite, Fe3.25Co0.75Sb12 (FeCoSb), compound was synthesized using a chemical alloying route. Nano-Cu2Se, and (nano-Cu2Se)1−x(nano-FeCoSb)x composites, where x = 0.05 and 0.1, were prepared via mechanical alloying followed by Spark Plasma Sintering process. Structural properties were evaluated by PXRD and SEM analysis, while the high temperature transport properties were examined via electrical conductivity, Seebeck coefficient, and thermal conductivity measurements in the temperature range of 300–800 K. Powder X-ray diffraction (PXRD) confirmed a single phase of nano Cu2Se, while the samples with FeCoSb inclusion consist of two phases as Cu2Se and CoSb3. SEM micrographs of all samples show that Cu2Se has randomly oriented grains with different sizes. Cu2Se samples with a FeCoSb inclusion show a rather different structure. In these samples, a rod-shaped FeCoSb phase, with a size varying between 20 and 100 nm, showed an inhomogeneous distribution in the structure and stacked between the Cu2Se layers. Transport data indicate that crystal mismatch between Cu2Se and FeCoSb has a strong effect on the TE transport properties. Electrical conductivity decreases but Seebeck coefficient enhances with nano FeCoSb inclusion. Total thermal conductivity was suppressed by 30% and ZT value enhanced by 15% with 5% nano FeCoSb inclusion at 750 K, likely due to a decrease in the electronic contribution of the thermal conductivity. Structural and transport data show that small amount of nanoinclusion of FeCoSb has a beneficial effect on the TE performance of nano Cu2Se at temperatures below 800 K.

Highlights

In an effort to reduce global warming, which results from the burning of fossil fuels, various alternative energy sources have been identified
Similar Powder X-ray diffraction (PXRD) pattern was obtained for Cu2Se sample with 2% nano FeCoSb inclusion
Detailed structural analyses of all samples were performed by SEM-EDS, PXRD, and transport properties were evaluated via Seebeck coefficient, electrical conductivity and thermal conductivity measurements

Summary

Introduction

In an effort to reduce global warming, which results from the burning of fossil fuels, various alternative energy sources have been identified. For more than a decade, this technology has not been used in a large scale, this is because of its inherent low conversion efficiency (Bell, 2008; Snyder et al, 2008; Julian Goldsmid, 2009). This conversion efficiency is proportional to the efficiency of the TE material, which can be determined by a factor called figure of merit Z. A good TE material should have a high power factor (S2σ) and a low thermal conductivity (Bell, 2008; Snyder et al, 2008; Julian Goldsmid, 2009). The PLEC concept could be successfully applied to copper-based chalcogenides (Ballikaya et al, 2013)

Methods

Results

Conclusion