The role of nanoscale defect features in enhancing the thermoelectric performance of p-type nanostructured SiGe alloys

Abstract

Despite SiGe being one of the most widely studied thermoelectric materials owing to its application in radioisotope thermoelectric generators (RTG), the thermoelectric figure-of merit (ZT) of p-type SiGe is still quite low, resulting in poor device efficiencies. In the present study, we report a substantial enhancement in ZT∼ 1.2 at 900 °C for p-type nanostructured Si80Ge20 alloys by creating several types of defect features within the Si80Ge20 nanostructured matrix in a spectrum of nano to meso-scale dimensions during its nanostructuring, by employing mechanical alloying followed by spark plasma sintering. This enhancement in ZT, which is ∼25% over the existing state-of-the-art value for a p-type nanostructured Si80Ge20 alloy, is primarily due to its ultralow thermal conductivity of ∼2.04 W m(-1) K(-1) at 900 °C, resulting from the scattering of low-to-high wavelength heat-carrying phonons by different types of defect features in a range of nano to meso-scale dimensions in the Si80Ge20 nanostructured matrix. These include point defects, dislocations, isolated amorphous regions, nano-scale grain boundaries and more importantly, the nano to meso-scale residual porosity distributed throughout the Si80Ge20 matrix. These nanoscale multi-dimensional defect features have been characterized by employing scanning and transmission electron microscopy and correlated with the electrical and thermal transport properties, based on which the enhancement of ZT has been discussed.

The effect of YSi2 nanoinclusion on the thermoelectric properties of p‐type SiGe alloy

“…The SiGe nano‐grains can scatter phonon effectively but show a minimum effect on the electrical transport since the phonon mean free path (MFP) is larger than charge carrier MFP. The ZT values were demonstrated to be as large as 1.84 and 1.2 for n‐ and p‐type SiGe alloys, respectively.…”

“…In the last decade, the enhanced ZT values of SiGe alloys have been reported continuously exploiting a nanostructuring approach . The idea of this approach is to reduce grain sizes of SiGe to a few ten nanometers.…”

Mechanical properties and microstructure of spark plasma sintered nanostructured p-type SiGe thermoelectric alloys

“…GPa, κ=2.04 W/mK [69] and α [70], ν [71] values were taken from the literature of similar alloy composition. The value of thermal shock resistance parameter was found to be ~ 391 ± 21 Wm -1 and this value is comparable or better than those reported for other state-of-the-art TE materials [20,29,36] as shown in Fig.…”

Optimizing the Dopant and Carrier Concentration of Ca5Al2Sb6 for High Thermoelectric Efficiency

“…Thus, thermoelectric devices have the advantages of being solid-state devices, low maintenance costs and long lifetime3. Currently, the two main focuses in thermoelectrics research are the discovery of new materials with high thermoelectric efficiency45678 and the design and optimization of thermoelectric generators9101112. Our work focuses on materials optimization for thermoelectric applications.…”