First-principles calculations to investigate thermoelectric, thermophysical, and optical properties of RNi₄P₁₂ (R = Sm, Eu) rare-earth metal skutterudites

This study presents a comprehensive investigation into the intrinsic properties of RNi₄P₁₂ (where R = Sm, Eu) filled skutterudite, employing the full-potential linearized augmented plane wave method within density functional theory (DFT) simulations using the WIEN2k framework. Structural, phonon stability, mechanical, electronic, magnetic, transport, thermal, and optical properties are thoroughly explored to provide a holistic understanding of these materials. Initially, the structural stability of SmNi₄P₁₂ and EuNi₄P₁₂ is rigorously evaluated through ground-state energy calculations obtained from structural optimizations, revealing a preference for a stable ferromagnetic phase over competing antiferromagnetic and non-magnetic phases. Electronic properties are further investigated using a combination of computational schemes, including Generalized Gradient Approximation (GGA) and Trans-Bhalla modified Becke Johnson (TB-mBJ), effectively handling the f-electrons. Both approximations reveal intriguing metallic behavior in both spin-up and spin-down channels. The focus is on Ni-P-based filled skutterudite, featuring localized 4f and 5d-electrons, which exhibit dense energy bands near the Fermi energy, originating from rare earth and Ni-atoms. The dense density of states near the Fermi energy suggests suitability for thermoelectric applications. Additionally, spin-polarized band structures unveil significant net magnetism, indicating potential applications in spintronics. Elastic parameters are estimated using the Voigt-Reuss-Hill approximation, with elastic stability crucial for practical applications, characterized by brittleness indicating the compounds' ability to deform without fracturing under stress. Finally, transport and thermal properties are analyzed, providing insights into conductivity and heat dissipation characteristics. Optical constants, including dielectric function, optical reflectivity, refractive index, electron energy loss, and optical conductivity, are calculated for photon energy radiation. Overall, this study offers a comprehensive understanding of the multifaceted properties of SmNi₄P₁₂ and EuNi₄P₁₂-filled skutterudite, laying the groundwork for their potential applications in various fields.