DFT analysis of rare-earth double perovskite oxides KXSn2O6 (X = Pr, Nd)

In this study, we employ density functional theory (DFT) to investigate the structural, electronic, optical, elastic, magnetic, and thermal properties of rare-earth-based double perovskite oxides KXSn₂O₆ (X = Pr, Nd). Both compounds crystallize in the cubic Fm3 $\overline{̅m}$ space group, with optimized lattice constants of 8.243 Å (KPrSn₂O₆) and 8.215 Å (KNdSn₂O₆). Their structure comprises corner-sharing SnO₆ octahedra and A-site Pr/Nd ions forming mixed ionic-covalent bonds. Negative formation energy, phonon dispersion, and the Birch–Murnaghan equation of state confirm structural stability. Electronic band structures using the mBJ potential show spin-polarized indirect semiconducting gaps of 2.095 eV (Pr) and 2.374 eV (Nd) in the spin-down channel. The valence band is dominated by O-2p states, while conduction bands involve Sn-5p/5d and Pr/Nd-4f orbitals, suggesting optoelectronic and spintronic utility. Strong UV absorption begins at 2.2–2.5 eV, with absorption peaks in the range of 6 eV–13 eV KPrSn₂O₆ exhibits higher optical constants (n ≈ 6.6, R ≈ 68 %) than KNdSn₂O₆ (n ≈ 1.9, R ≈ 45 %). Elastic constants validate mechanical stability, with Young's moduli of 280 GPa (Pr) and 270 GPa (Nd), and Pugh's ratios indicating ductility. Magnetic analysis reveals total moments of 2.00 μB (Pr) and 2.99 μB (Nd), mainly from rare-earth 4f-electrons. Thermal assessments show Debye temperatures of 581 K (Pr) and 567 K (Nd), indicating strong lattice stiffness and high melting points. These findings highlight KXSn₂O₆ as a promising multifunctional candidate for UV optoelectronics, spintronics, and high-temperature electronics.