First principles investigation of structural, mechanical, thermodynamic, and electronic properties of Al-based perovskites XAlH3 (X=K, Rb, Cs) for hydrogen storage

First-principles calculations have been used to study the structural, mechanical, and hydrogen storage properties of the perovskite hydrides, XAlH3 (X = K, Rb, and Cs). The simulated pattern of X-ray diffraction (XRD) also confirmed their polycrystalline structure. The investigation of hydrogen storage properties has led to the determination of gravimetric hydrogen storage capacities for KAlH3, RbAlH3, and CsAlH3, which are found to be 4.38, 2.62, and 1.86 wt%, respectively. Furthermore, the hydrogen desorption temperatures are determined to be 448.43, 507.96, and 487.22K for KAlH3, RbAlH3, and CsAlH3, respectively. The calculation of elastic constants has confirmed that these compounds are mechanically stable. The computed elastic constants have determined the bulk modulus, Young's modulus, shear modulus, and Poisson's ratio. Using ELATE software, 3D visualization of anisotropic elastic properties i.e., maximum and minimum values of Young's modulus, linear compressibility, shear modulus, and Poisson's ratio along with anisotropic factors have been analyzed. Thermodynamic properties involving entropy, Debye temperature, specific heat capacity at constant pressure, and coefficient of thermal expansion have also been calculated. The electronic properties of these compounds confirmed their metallic behavior. These findings provide insight into Al -based perovskite hydrides and their potential applications for hydrogen storage perspectives.