Designing new Zintl phases SrBaX (X = Si, Ge, Sn) for thermoelectric applications using \textit{ab initio} techniques

TL;DR

This study uses ab initio calculations to design and analyze new Zintl phases SrBaX (X=Si, Ge, Sn) with exceptionally low thermal conductivities and high thermoelectric efficiency, comparable to leading materials like SnSe.

Contribution

The paper introduces a computational design of novel SrBaX Zintl phases, revealing their promising thermoelectric properties and low thermal conductivities through first-principles simulations.

Findings

Low lattice thermal conductivities (<1 W/mK) in SrBaX materials.

High thermoelectric figure of merit (ZT~2.0 at 700K) for SrBaGe.

Both p- and n-type doping show similar performance.

Abstract

Slack's phonon-glass and electron-crystal concept has been the guiding paradigm for designing new thermoelectric materials. Zintl phases, in principle, have been shown as great contenders of the concept and thereby good thermoelectric candidates. With this as motivation, we design new Zintl phases SrBaX (X = Si, Ge, Sn) using state-of-the-art computational methods. Herein, we use first-principles simulations to provide key theoretical insights to thermal and electrical transport properties. Some of the key findings of our work feature remarkably low lattice thermal conductivities ($<$~1~W~m$^{-1}$~K$^{-1}$), putting proposed materials among the well-known thermoelectric materials such as SnSe and other contemporary Zintl phases. We ascribe such low values to antibonding states induced weak bonding in the lattice and intrinsically weak phonon transport, resulting in low phonon velocities, short lifetimes, and considerable anharmonic scattering phase spaces. Besides, our results on electronic structure and transport properties reveal tremendous performance of SrBaGe ($ZT\sim$ 2.0 at 700~K), highlighting the relevance among state-of-the-art materials such as SnSe. Further, the similar performances for both $p$- and $n$-type dopings render these materials attractive from device fabrication perspective. We believe that our study would invite experimental investigations for realizing the true thermoelectric potential of SrBaX series.