Ab-initio calculations of the elastic and finite-temperature thermodynamic properties of niobium- and magnesium hydrides

•Elastic properties of MgH2 and NbH are calculated by using DFT calculations.•Thermodynamic properties of MgH2 and NbH are predicted by using DFT calculations.•Calculations confirm destabilizing of Mg/Nb multilayers due to mechanical stresses.•Understanding of enhancement of hydrogen desorption in Mg/Nb films is achieved.•Idea of choosing the constituents of multilayers for storing hydrogen is proposed.

Density Functional Theory (DFT) calculations have been used for calculating the elastic and thermodynamic properties of Mg, Nb, and their hydrides. The study is motivated by a previous work that showed constraints arising from Mg/Nb layer interfaces de-stabilized the magnesium hydride and resulted in decomposition temperatures much lower than in the bulk state. The calculated mechanical properties and the difference in the volume expansion of Mg- and Nb-hydrides support the ideas of large, de-stabilizing mechanical stresses arising from significant volume expansion incompatibilities in Mg/Nb multilayers. The stress and corresponding formation of metastable phases result in significant destabilization of MgH2 and provide ultra-low hydrogen desorption temperature in Mg/Nb multilayers.