Effect of hydrostatic pressure and alloying on thermoelectric properties of van der Waals solid KMgSb: An ab initio study

Using a combined approach of first-principles and Boltzmann transport theory, we conducted a systematic investigation of the thermal and electrical transport properties of the unexplored ternary quasi-two-dimensional KMgSb system of the $\mathrm{KMg}X$ ($X=\mathrm{P},\mathrm{As},\mathrm{Sb}, \text{and} \mathrm{Bi}$) family. In this paper, we present the transport properties of KMgSb under the influence of hydrostatic pressure and alloy engineering. At a carrier concentration of $\ensuremath{\sim}8\ifmmode\times\else\texttimes\fi{}{10}^{19}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$, we observed a close match in the figure of merit (zT; $\ensuremath{\sim}0.75$, at 900 K) for both $n$-type and $p$-type KMgSb, making it an attractive choice for engineering thermoelectric devices with uniform materials in both legs. This characteristic is particularly advantageous for high-performance thermoelectric applications. Additionally, as pressure decreases, the zT value exhibits an increasing trend, further enhancing its potential for use in thermoelectric devices. Substitutional doping (replacing 50% of Sb atoms with Bi atoms) resulted in a significant $\ensuremath{\sim}49%$ (in-plane) increase in the peak thermoelectric figure of merit. Notably, after alloy engineering, the maximum figure-of-merit value obtained reached $\ensuremath{\sim}1.45$ at 900 K temperature. Hydrostatic pressure emerges as an effective tool for tuning the lattice thermal conductivity ${\ensuremath{\kappa}}_{L}$. Our observations indicate that negative-pressure-like effects can be achieved through the chemical doping of larger atoms, especially when investigating ${\ensuremath{\kappa}}_{L}$ properties. Through our computational investigation, we elucidate that hydrostatic pressure and alloy engineering hold the potential to dramatically enhance thermoelectric performance in this compound.