Neutron-Shielding Metallic RE ₃ AlN (RE = Er, Tm, Yb) Nitrides: First-Principles and Monte Carlo Insights for Advanced Functional Materials

A comprehensive first-principles investigation within the GGA+U framework was performed to explore the structural, electronic, magnetic, thermodynamic, and optical properties of the inverse perovskite nitrides Er 3 AlN, Tm 3 AlN, and Yb 3 AlN. To the best of our knowledge, this study represents the first systematic and comparative analysis of these late rare-earth anti-perovskite nitrides, addressing the lack of detailed understanding of their fundamental properties. The results confirmed that all compounds are thermodynamically stable in a cubic structure, with optimized lattice parameters in the range of 4.78–4.80 Å. Electronic structure calculations revealed a metallic nature for all systems, accompanied by a ferromagnetic ground state, particularly pronounced in Tm.AlN, highlighting their potential for spin-dependent applications. The calculated bulk moduli (64.1–69.3 GPa) indicated good mechanical stability. Optical analysis showed strong responses in the ultraviolet region (4–8 eV), associated with interband transitions and metallic reflectivity. Furthermore, complementary neutron-transport simulations demonstrated enhanced neutron absorption capabilities, with a performance trend of Er 3 AlN > Tm 3 AlN > Yb 3 AlN, supporting their relevance in radiation-tolerant environments. Overall, the combination of metallicity, magnetic ordering, thermal stability, and optical activity establishes these materials as promising candidates for advanced functional applications, including spintronics, UV optoelectronics, and radiationresistant technologies.