Is LiI a Potential Dopant Candidate to Enhance the Thermoelectric Performance in Sb-Free GeTe Systems? A Prelusive Study

Bhuvanesh Srinivasan,David Berthebaud,Takao Mori

doi:10.3390/en13030643

Bhuvanesh Srinivasan, David Berthebaud + Show 1 more

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https://doi.org/10.3390/en13030643

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Abstract

As a workable substitute for toxic PbTe-based thermoelectrics, GeTe-based materials are emanating as reliable alternatives. To assess the suitability of LiI as a dopant in thermoelectric GeTe, a prelusive study of thermoelectric properties of GeTe1−xLiIx (x = 0–0.02) alloys processed by Spark Plasma Sintering (SPS) are presented in this short communication. A maximum thermoelectric figure of merit, zT ~ 1.2, was attained at 773 K for 2 mol% LiI-doped GeTe composition, thanks to the combined benefits of a noted reduction in the thermal conductivity and a marginally improved power factor. The scattering of heat carrying phonons due to the presumable formation of Li-induced “pseudo-vacancies” and nano-precipitates contributed to the conspicuous suppression of lattice thermal conductivity, and consequently boosted the zT of the Sb-free (GeTe)0.98(LiI)0.02 sample when compared to that of pristine GeTe and Sb-rich (GeTe)x(LiSbTe2)2 compounds that were reported earlier.

Highlights

IntroductionThe efficiency of a TE material is quantified by a dimensionless figure of merit, zT = S2 σT/κ, where σ, S, T and κ are the electrical conductivity, Seebeck coefficient, absolute temperature and total thermal conductivity (which constitute both the electronic part, κe , and the lattice part, κlatt ), respectively
Thermoelectric (TE) materials and devices have gained limelight due to their ability to reversibly convert waste heat into useful electricity, especially for energy harvesting applications [1,2,3].The efficiency of a TE material is quantified by a dimensionless figure of merit, zT = S2 σT/κ, where σ, S, T and κ are the electrical conductivity, Seebeck coefficient, absolute temperature and total thermal conductivity, respectively.These transport properties are highly interlinked and there is a greater challenge in decoupling the electrical and thermal transport parameters [4]
The sharp reflections noticed from the X-ray diffraction (XRD) patterns for (GeTe)1-x (LiI)x (x = 0–0.02) stipulate the phases to be crystalline in nature (Figure 1)

Summary

Introduction

The efficiency of a TE material is quantified by a dimensionless figure of merit, zT = S2 σT/κ, where σ, S, T and κ are the electrical conductivity, Seebeck coefficient, absolute temperature and total thermal conductivity (which constitute both the electronic part, κe , and the lattice part, κlatt ), respectively These transport properties are highly interlinked and there is a greater challenge in decoupling the electrical and thermal transport parameters [4]. GeTe-based materials have emerged as viable alternatives, as they have proven to exhibit higher TE performance (zT > 1), if optimally alloyed/doped with appropriate elements [19] Such strategies have been effectively adopted on several classes of GeTe-based materials to improve their electrical transport properties (i.e., the power factor, S2 σ) by the convergence of electronic band valleys [20,21] or by the introduction of resonance states [22,23], and/or to suppress their thermal transport properties by nanostructuring [24].

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