Thermoelectric properties of Fe${}_2$VAl at high temperature region: A combined experimental and theoretical study

Abstract

Heusler type compounds have long been recognized as potential thermoelectric (TE) materials. Here, the experimentally observed TE properties of Fe${}_2$VAl are understood through electronic structure calculations in the temperature range of $300-800$ K. The observed value of $S$ is $\sim -$138 $\hat{I}¼$V/K at 300 K. Then, the $|S|$ decreases with increase in temperature up to the highest temperature with the value of $\sim -$18 $\hat{I}¼$V/K at 800 K. The negative sign of $S$ in the full temperature window signifies the dominating $n$-type character of the compound. The temperature dependent of electrical conductivity, $\ddot{I}ƒ$ (thermal conductivity, $\hat{I}º$) exhibits the increasing (decreasing) trend with the values of $\sim$1.2 $\times$ 10${}^5$ $\hat{I}{\text{c◯}}^{-1}$m${}^{-1}$ ($\sim$23.7 W/m-K) and $\sim$2.2 $\times$ 10${}^5$ $\hat{I}{\text{c◯}}^{-1}$m${}^{-1}$ ($\sim$15.3 W/m-K) at 300 K and 800 K, respectively. In order to understand these transport properties, the DFT based semi-classical Boltzmann theory is used. The contributions of multi-band electron and hole pockets are found to be mainly responsible for the temperature dependent trend of these properties. The decrement of $|S|$ and increment of $\ddot{I}ƒ/\ddot{I}„$ $\&$ $\hat{I}{º}_e/\ddot{I}„$ ($\ddot{I}„$ is relaxation time) with temperature is directly related with the contribution of multiple hole pockets. Present study suggests that DFT based electronic calculations provide reasonably good explanations of experimental TE properties of Fe${}_2$VAl in the high temperature range of $300-800$ K.