First-principles study on the electronic, mechanical, vibrational, thermodynamic, and optical properties of TiFe and its Hydrides (TiFeHx, x = 1, 2, 4)
Y. Chnika, Abderrahim Jabar, L. Bahmad, Rachid Ahl Laamara
Abstract
We investigate TiFe and its hydrogenated derivatives, TiFeH, TiFeH 2 , and TiFeH 4 , using density functional theory (DFT) to evaluate their potential as solid-state hydrogen storage materials. Structural, mechanical, electronic, thermodynamic, vibrational, and optical properties were analyzed using the Quasi-Harmonic Approximation (QHA) and Density Functional Perturbation Theory (DFPT) frameworks. Hydrogenation induces lattice expansion and symmetry reduction while preserving mechanical and vibrational stability, as confirmed by the Born criteria and phonon spectra free of imaginary modes. All TiFeH x compounds are thermodynamically favorable and ductile. A temperature-dependent Gibbs free energy approach was used to estimate desorption behavior, yielding desorption temperatures of approximately 450 K for TiFeH, 510 K for TiFeH 2 , and 557 K for TiFeH 4 under 10 bar H 2 pressure. TiFeH 4 , in particular, offers a gravimetric hydrogen capacity of 3.74 wt%, highlighting its promise for high-capacity storage. Additionally, hydrogen incorporation modifies the dielectric response and enhances optical absorption, suggesting potential for complementary functionality in thermal regulation and hydrogen sensing applications. These findings provide predictive insight into the design of stable, efficient TiFe-based hydrides and offer theoretical guidance for future experimental development.