Unveiling the Magnetic Ordering, Structural Phase Transition, Dynamical Stability, and Optoelectronic Properties of Orthorhombic Fluoro‐Perovskite NaCoF ₃

Fluoro-perovskites have attracted considerable attention due to their distinct and adjustable electronic, magnetic, and optical properties. In this work, a comprehensive first-principles study based on density functional theory is carried out to investigate the physical properties of NaCoF₃ in the orthorhombic Pnma and Cmcm phases. The results reveal that the perovskite (Pnma) phase is the ground-state structure, exhibiting a G-type antiferromagnetic configuration. Enthalpy calculations indicate a pressure-induced phase transition to the post-perovskite (Cmcm) phase at a static pressure of 8.28 GPa at 0 K, with the stability domain of the post-perovskite phase decreasing as temperature increases. Phonon dispersion analysis confirms the dynamical stability of the Pnma phase, while the Cmcm phase is stable only under external thermodynamic conditions. The Co-3d orbitals are highly influenced by the correlation effects on the electronic structure. There is intense polarization and a high absorption in the 4.0-5.0-eV range, as well as a significant anisotropy in the dielectric function and refractive index. The structural stability, antiferromagnetic ordering, insulating behavior, and anisotropic optical response of NaCoF₃ make it an interesting candidate in the formation of antiferromagnetic data-storage devices and ultraviolet optoelectronic applications.