Thermoelectric materials

Thermoelectric materials

Thermoelectrics have attracted increasing attention as a sustainable and flexible source of electricity able to meet a wide range of power requirements. Their application is wide as they could be used in automotive, aerospace and medical fields, and wherever temperature gradients exist. In this project we focus mostly on the ternary Ag–Sb–Te system as it is a promising thermoelectric material. The investigated compounds possess moderate to high ZT-values depending on their microstructure.

The conversion efficiency of TE materials is determined by the dimensionless figure of merit, ZT, which depends on the thermal and electrical conductivity, the Seebeck coefficient and the temperature. The achieved efficiency is related to the micro-/nanostructure of the investigated alloy which can be modified by the processing parameters and doping. The micro/nanostructure is studied in depth in the project by electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), focused ion beam (FIB) and atom probe tomography (APT).

The studied Ag-Sb-Te alloys are prepared by our project partners from the Technion by melting high purity elemental silver, antimony and telluride followed by a special annealing, homogenization and heat treatment to achieve a high precipitation level. The aim is to optimize the ZT by creating phase/grain boundaries to reduce the lattice thermal conductivity, while maintaining relatively high values of electrical conductivity.

EBSD, SEM, APT and TEM investigations show the presence of several metastable lamellar structures of Sb-Te rich precipitates which evolve toward the Sb2Te3 phase. These structural and chemical information are essential in understanding the mechanism for the efficiency improvement and thus to further design better TE materials.

SEM micrograph and corresponding elemental distribution of Ag, Sb and Te  showing multiple Sb,Te-rich precipitates embedded in the AgSbTe2 matrix.

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