Insights of physical properties of alkaline earth metal-based (X=Ba, Mg, Sr, Ca) complex X3H8Ru hydrides, for multifunctional energy conversion devices

This study focuses on first-principles investigation to analyze the multifunctionality of alkaline earth metal substitution in ruthenium-based complex hydrides ([Formula: see text], where [Formula: see text], Mg, Sr, Ca) for solar cell and hydrogen storage applications. Geometrical optimization has provided the equilibrium ground-state lattice parameters, which have proven the stability of compounds, by phonon dispersion analyses and phonon density of states (DOS). Charge analysis by Mulliken and Hirshfeld schemes has provided the significant details about the net charge transfer from alkaline earth metals toward Ru[Formula: see text] and H[Formula: see text] atoms, and electron localization function (ELF) analysis has presented mixed ionic–covalent bonding with strong electron localization around Ru[Formula: see text] and H[Formula: see text] regions. All these hydrides are naturally semiconductors as revealed by electronic analysis, with band gap values from 0.55[Formula: see text]eV to 2.58[Formula: see text]eV, mainly due to [Formula: see text] atom hybridization near the Fermi level and substitution of alkaline earth metal series. Optical analysis has demonstrated the high absorption coefficient ([Formula: see text] [Formula: see text]cm[Formula: see text]) followed by relatively large real dielectric function ([Formula: see text]) of values around 7–9, refractive index ([Formula: see text]) of 2.5–3.2, indicating strong light–matter interaction, which are presenting the possible potential of hydrides in optoelectronics and photovoltaic devices. Increasing trends in [Formula: see text] entropy and enthalpy with decreasing trends of free energy curves for hydrides are indicating that these materials are real solids in nature. Elastic constant values for the hydrides have satisfied the Born stability criteria, hence proving the mechanical robust and ductility ([Formula: see text]). Hydrogen storage ratios of hydrides are 1.55%, 4.43%, 2.17%, and 3.52% for [Formula: see text]H 8 Ru ([Formula: see text], Mg, Sr, Ca) compounds making them effective for hydrogen storage applications.