Phase stability and mechanical properties of niobium dihydride

First-principles calculation shows that the NbH sub(x) phases (1 less than or equal to x less than or equal to 2) with face-centered cubic (FCC), orthorhombic (FCO), and tetragonal (FCT) modifications are all energetically favorable with negative heats of formation, while FCC NbH sub(1) and NbH sub(1.25) could not be formed due to their mechanical unstableness. It is also revealed that FCT and FCO could coexist in NbH sub(1) and NbH sub(1.25), FCC and FCT coexist in NbH sub(1.5) and NbH sub(1.75), while only FCC in NbH sub(2). Calculations also indicate that the magnitude of the elastic moduli of NbH sub(x) phases at each H concentration is as follows: E > B > G, and the G, E, and G/B values of NbH sub(x) phases reach a minimum when x = 1.5. Moreover, electronic structures are discussed to provide a deep understanding of various properties, and the derived results are in good agreement with similar experimental evidence in the literature.