First-Principles Investigation of Structural and Thermoelectric Properties of KXH

In this work, we present a comprehensive first-principles study of the structural, electronic, thermal, and thermoelectric properties of perovskite hydrides KXH3 (X = Al, Mn, and Ni). Calculations were performed within the framework of density functional theory combined with semiclassical Boltzmann transport theory. Structural analysis confirms the stability of all compounds in the cubic perovskite phase. The electronic band structures and density of states reveal that all three compounds exhibit metallic behavior. In particular, KAlH3 shows a pseudo-gap-like feature near the Fermi level with a low but finite density of states, indicating a weak metallic character, while KMnH3 and KNiH3 display pronounced metallic properties due to significant contributions of transition-metal d orbitals near the Fermi level. The electrical and thermal conductivities increase with temperature for all compounds, with KAlH3 exhibits relatively high electrical conductivity despite its low density of states at the Fermi level. Thermoelectric performance analysis shows an enhancement of the power factor and figure of merit (ZT) at elevated temperatures, with KMnH3 achieving the best performance due to a favorable balance between electrical conductivity, Seebeck coefficient, and thermal conductivity. These results highlight the crucial role of chemical substitution at the X-site in tuning the electronic and transport properties of KXH3 hydrides, making them promising candidates for high-temperature thermoelectric applications.