Ab initio study of phononic thermal conduction in ScAgC half-Heusler

Abstract

We present a first-principles lattice calculations to comprehend the thermal expansion $\alpha(T)$ and lattice thermal conductivity $\kappa_{ph}$ of ScAgC. The obtained positive frequencies of phonon dispersion shows the dynamical stability of ScAgC in FCC structure. The estimated $\alpha(T)$ from quasi-harmonic approximation (QHA) at 300(1200) K is $\sim$4(4.6)$\times$$10^{-6}$ K$^{-1}$. The predicted value of total $\kappa_{ph}$ from phonon-phonon interaction (PPI) at 300(1200) K is $\sim$7.4(1.8) Wm$^{-1}$K$^{-1}$. The highest group velocity for acoustic $\&$ optical branches (AB $\&$ OB) is $\sim$6.7 and $\sim$3.5 km/s, respectively. The predicted average phonon lifetime ($\tau_{\lambda}$) for AB(OB) is $\sim$2.5(1.65) ps at 300 K, whereas it is $\sim$0.6(0.4) ps at 1200 K. The estimated highest heat capacity ($C_{\lambda}$) at 200 K for AB(OB) is $\sim$23.5 (19.5) meV/K. We fitted the equation $A_{\kappa}$T$^{-x_{\kappa}}$($A_{\tau}$T$^{-x_{\tau}}$) in the $\kappa_{ph}$($\tau_{\lambda}$) curve to gain a thorough understanding of temperature-dependent $\kappa_{ph}$ trend. The $x_{\kappa}$ for total branches is calculated to be $\sim$1.02. The $x_{\tau}$ value due to total AB(OB) is estimated to be $\sim$1.04(1.02), while it is $\sim$1.03 for total branches. The calculated $x_{\kappa}$ for total AB(OB) is $\sim$1.04(0.95), implying that AB contributes more to the total $\kappa_{ph}$. This research could be important for enhancing the properties of ScAgC regarding thermoelectric and photovoltaic applications.