Thermal Conductivity Reduction of Fe2VAl Thermoelectric Alloys Through Atomotic Disorder Engineering

Understanding the fundamental thermal transport is crucial to tuning thermal conductivity, an important factor in high efficiency of a thermoelectric material. Fe2VAl has emerged as a promising thermoelectric material due to its non-toxicity, narrow bandgap, and cost-effectiveness, making it suitable for high-efficiency energy conversion applications. This study investigates the impact of both n-type(Germanium) and p-type(Aluminum) dopants on the thermal conductivity of Fe2VAl, aiming to optimize its thermoelectric performance. Through engineering disorder in the compound in particular by doping with germanium we demonstrate a significant reduction in thermal conductivity. The base alloy Fe2VAl has thermal conductivity of ~25W/K-m at 300K, while the doped Fe2VAl0.9Ge0.1 has a thermal conductivity of less than 5W/K-m at 300K. Furthermore, the temperature-dependent thermal conductivity shows a behavior similar to amorphous materials such as fused silica .This reduction is attributed to enhanced atomic disorder within the material. Furthermore, we explore the fundamental mechanisms of thermal conductivity and atomic disordering and its impact on lattice dynamics by fitting temperature-dependent thermal conductivity measurements from 10K to 600K. By analyzing the combined effects of off-stoichiometric composition and heat treatments, we elucidate how factors such as alloying and disorder lead to a drastic reduction in thermal conductivity. This is achieved by considering diagonal and off-diagonal transport mechanisms and incorporating electron-phonon scattering enhanced by band structure modification upon atomic disordering into the Callaway Model, in addition to point defect scattering and boundary scattering. Our findings provide insights into the pathways for achieving low thermal conductivity in Fe2VAl and highlight the potential of tailoring thermal properties through a strategic combination doping and heat treatments, advancing the development of high-performance and economically viable thermoelectric materials.