First-principles study of novel Cs₂LuCoH₆ and Cs₂LuZnH₆ double hydride perovskites for hydrogen storage applications

This work presents a comprehensive evaluation of the structural, electronic, vibrational, magnetic, and mechanical characteristics of the double hydride perovskites Cs₂LuCoH₆ and Cs₂LuZnH₆, with the aim of determining their potential for hydrogen storage and related energy applications. The fully relaxed and optimized structures exhibit negative cohesive energies of -3.57 eV per atom for Cs₂LuCoH₆ and -2.65 eV per atom for Cs₂LuZnH₆, confirming their thermodynamic stability. Electronic band structure analysis reveals semiconductor behavior with an energy band gap of 0.917 eV for Cs₂LuCoH₆, while Cs₂LuZnH₆ displays metallic behavior with a zero band gap. Phonon dispersion calculations confirm the dynamic stability of Cs₂LuCoH₆, showing no imaginary modes, whereas Cs₂LuZnH₆ exhibits a few negative phonon frequencies, indicating partial instability. Magnetic analysis demonstrates a ferromagnetic phase with an overall magnetic moment of 1.25 µB for Cs₂LuCoH₆ and nonmagnetic behavior for Cs₂LuZnH₆. The computed hydrogen storage capacities (by weight) are 4.87 wt% for Cs₂LuCoH₆ and 4.46 wt% for Cs₂LuZnH₆. The tolerance factors (0.92 for Cs₂LuCoH₆ and 0.84 for Cs₂LuZnH₆) further confirm the structural symmetry and mechanical robustness of these compounds. These DFT-based results suggest that Cs₂LuCoH₆ and Cs₂LuZnH₆ are promising and novel candidates for use in next-generation hydrogen storage devices and energy-related applications.