Critical Reassessment of the H–Nb System and Experimental Investigation and Thermodynamic Modeling of the H–Nb–Zr System

The phase diagram and thermodynamic data of the H–Nb system are evaluated and re-assessed to improve the description of this system. This system is modeled up to a few MPa. Only the gas phase and the solid phases are considered in the present study. Since only a few data were available for the H–Nb–Zr ternary system, a new set of experimental data has been obtained in the present work. For the first time, the solubility of niobium into the ε-ZrH2 phase is found. In addition, Density Functional Theory calculations and the Special Quasirandom Structures method are used to determine the formation enthalpies of all the compounds and the mixing enthalpies in the different phases, respectively. Finally, the literature data as well as our experimental and calculated data are used for the Calphad modeling of the H–Nb–Zr system.