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, power plants 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 (TE) material that can be used to convert waste heat into electrical energy. The Ag-Sb-Te compounds possess high ZT-values and are subsystems of the very promising quaternary compounds Pb-Ag-Sb-Te (LAST) and (AgSbTe2)1-x(GeTe)x (TAGS).
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.
![Figure 1: The carrier mobility as a function of grain size and composition. EBSD maps of Nb0.95Ti0.05FeSb and Nb0.80Ti0.20FeSb revealing the different grain sizes. In addition, high resolution STEM image and APT data of the grain boundary complexion are shown. Data from [1].](/4718537/original-1737641784.jpg?t=eyJ3aWR0aCI6ODQ4LCJmaWxlX2V4dGVuc2lvbiI6ImpwZyIsIm9ial9pZCI6NDcxODUzN30%3D--b63a355646c0951d7ed405c8160dd004c8baa644 "Figure 1: The carrier mobility as a function of grain size and composition. EBSD maps of Nb0.95Ti0.05FeSb and Nb0.80Ti0.20FeSb revealing the different grain sizes. In addition, high resolution STEM image and APT data of the grain boundary complexion are shown. Data from [1].")
![Figure 1: The carrier mobility as a function of grain size and composition. EBSD maps of Nb0.95Ti0.05FeSb and Nb0.80Ti0.20FeSb revealing the different grain sizes. In addition, high resolution STEM image and APT data of the grain boundary complexion are shown. Data from [1].](/4718537/original-1737641784.jpg?t=eyJ3aWR0aCI6MjQ2LCJvYmpfaWQiOjQ3MTg1Mzd9--8198f9dfd1fd4b28de5d5cb7fb5bf0cf5fd3af1b)