Effect of hydrostatic pressure and alloying on thermoelectric properties of van der Waals solid KMgSb: An \textit{ab-initio} study

TL;DR

This study uses first-principles calculations to explore how hydrostatic pressure and alloying affect the thermoelectric properties of KMgSb, revealing ways to enhance its efficiency for thermoelectric applications.

Contribution

It provides the first systematic analysis of pressure and alloying effects on KMgSb's thermoelectric performance, showing significant improvements in zT values.

Findings

zT of ~0.75 at 8x10^{19} cm^{-3} carrier concentration

49% increase in zT with Bi alloying at 900 K

Pressure decreases enhance thermoelectric performance

Abstract

Through a combined first-principles and Boltzmann transport theory, we systematically investigate the thermal and electrical transport properties of the unexplored ternary quasi two-dimensional KMgSb system of KMgX (X = P, As, Sb, and Bi) family. Herein, the transport properties of KMgSb under the application of hydrostatic pressure and alloy engineering are reported. At a carrier concentration of $\sim8\times10^{19}~\mathrm{cm^{-3}}$, the figure of merit zT ($\sim0.75$) for both the $n$-type and $p$-type of KMgSb closely matched, making it an attractive option for engineering both legs of a thermoelectric device using the same material. This is particularly desirable for high-performance thermoelectric applications. Furthermore, the zT value increases as pressure decreases, further enhancing its potential for use in thermoelectric devices. In the case of substitutional doping (replacing 50 \% Sb by Bi atom), we observed $\sim49~\%$ (in-plane) increase in the peak thermoelectric figure of merit (zT). The maximum zT value obtained after alloy engineering is $\sim1.45$ at 900~K temperature. Hydrostatic pressure is observed to be a great tool to tune the lattice thermal conductivity ($\kappa_L$). We observed that the negative pressure-like effects could be achieved by chemically doping bigger-size atoms, especially when $\kappa_L$ is a property under investigation. Through our computational investigation, we explain that hydrostatic pressure and alloy engineering may improve thermoelectric performance dramatically.