Investigation of mechanical properties of KCaH3 and KSrH3 orthorhombic perovskite hydrides under high pressure for hydrogen storage applications

First principles calculations have been adopted to explore ground-state and high-pressure properties of KCaH3 and KSrH3 orthorhombic perovskite hydrides for the purpose of solid-state hydrogen storage. Formation enthalpies of materials, structural and mechanical properties, electronic and hydrogen storage properties are computed and examined. The computed formation enthalpies and phonon frequencies of KCaH3 and KSrH3 indicate dynamical stability at 0 GPa. The gravimetric hydrogen densities of KCaH3 and KSrH3 are found to be 3.55 wt% and 2.28 wt%, respectively. Also, the hydrogen desorption temperatures are calculated as 449 K and 394 K for KCaH3 and KSrH3. Elastic constants for each phase and several parameters derived from elastic constants are computed and evaluated, such as bulk and Shear modulus. The B/G ratios of materials depict that both KCaH3 and KSrH3 are brittle materials. The electronic properties show band gaps for both materials at 0 GPa, confirming an insulating nature and as pressure increases the band gap shrinks for KCaH3 and disappears for KSrH3.