Phase stability and mechanical properties of niobium dihydride

First-principles calculation shows that the NbHx phases (1 ≤ x ≤ 2) with face-centered cubic (FCC), orthorhombic (FCO), and tetragonal (FCT) modifications are all energetically favorable with negative heats of formation, while FCC NbH1 and NbH1.25 could not be formed due to their mechanical unstableness. It is also revealed that FCT and FCO could coexist in NbH1 and NbH1.25, FCC and FCT coexist in NbH1.5 and NbH1.75, while only FCC in NbH2. Calculations also indicate that the magnitude of the elastic moduli of NbHx phases at each H concentration is as follows: E > B > G, and the G, E, and G/B values of NbHx 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.