First-principles investigation of MgTH3 (T = Y, Tc) hydride perovskites: Insights into structural, electronic, mechanical, and optical properties

This work presents a systematic first-principles investigation into the structural, electronic, mechanical, and thermodynamic properties of MgYH 3 and MgTcH 3 hydride perovskites using density functional theory (DFT) within the GGA-PBE framework. Both compounds stabilize in the cubic Pm–3 m phase, meeting established mechanical, thermodynamic, and dynamic stability criteria. Thermodynamic stability is confirmed by negative formation enthalpies of −2.11 eV/atom for both systems, while phonon dispersion calculations verify their dynamic stability. Electronic analysis reveals a metallic nature for both systems, primarily driven by significant hybridization between Mg‑s and transition‑metal T‑d (T = Y, Tc) states near the Fermi level. Mechanical evaluation indicates a ductile and anisotropic character, with MgTcH 3 exhibiting superior stiffness and hardness, evidenced by a bulk modulus of 123.79 GPa. The calculated gravimetric hydrogen storage capacities are 2.60 wt% for MgYH 3 and 2.41 wt% for MgTcH 3 . Critically, the hydrogen desorption temperature (T d ) was determined to be 1557 K for both systems. While MgTcH 3 maintains structural integrity at this threshold (T m = 2473 K), the required T d for MgYH 3 exceeds its calculated melting point of 1120 K, indicating a fundamental physical limitation for reversible solid-state release. Consequently, these materials are presented as thermodynamically stable model systems for exploring the impact of d‑orbital hybridization on lattice rigidity and high‑temperature stability, rather than viable candidates for near‑ambient hydrogen storage applications.