A holistic approach to understanding structural, magneto-electronic, thermoelectric, and thermodynamic properties of RhMnZ (Z = Si, Ge) half Heusler alloys

Abstract

This study thoroughly examines the structural, mechanical, thermal, electronic, optical, and thermoelectric properties of RhMnZ (Z = Si, Ge) half-Heusler compounds, which feature 18 valence electrons. Using density functional theory (DFT) within the WIEN2k computational framework, the ground-state properties of these compounds were determined to establish a foundational understanding of their physical characteristics. To further assess their thermoelectric potential, the Boltzmann transport equation was applied with the constant relaxation time approximation, allowing for precise calculations of thermal and electrical conductivity. Results indicate that the lattice constants of RhMnSi and RhMnGe span from 5.6394 Å to 5.7447 Å, highlighting consistent crystalline structures that lack band gaps, confirming their metallic nature. Detailed elastic and thermodynamic evaluations demonstrate that these compounds are mechanically stable, displaying ductile and anisotropic behavior. The study further reveals that thermal properties, including specific heat and entropy, tend to increase with the atomic number of Z, suggesting that RhMnGe may have a slightly higher heat capacity compared to RhMnSi. For thermal conductivity estimation, Slack's model was employed, indicating that these compounds possess high lattice thermal conductivity—a crucial factor for thermoelectric materials. The substantial figure of merit (ZT) observed in these compounds, especially at elevated temperatures, points to their potential efficiency in thermoelectric applications. The combination of high thermal conductivity, favorable mechanical stability, and robust thermoelectric properties identifies RhMnZ compounds as promising candidates for use in energy conversion technologies, particularly where efficient heat-to-electricity conversion is needed. This study thus lays the groundwork for future applications of RhMnSi and RhMnGe in thermoelectric devices.