Lu–H–N Phase Diagram from First-Principles Calculations

Employing a comprehensive structure search and high-throughput first-principles calculation method on 1561 compounds, the present study reveals the phase diagram of Lu–H–N. In detail, the formation energy landscape of Lu–H–N is derived and utilized to assess the thermodynamic stability of each compound that is created via element substitution. The result indicates that there is no stable ternary structure in the Lu–H–N chemical system, however, metastable ternary structures, such as Lu₂₀H₂N₁₇ (C2/m) and Lu₂H₂N ($P\overline{3}m1$), are observed to have small E_hull (< 100 meV/atom). It is also found that the energy convex hull of the Lu–H–N system shifts its shape when applying hydrostatic pressure up to 10 GPa, and the external pressure stabilizes a couple of binary phases such as LuN₉ and Lu₁₀H₂₁. Additionally, interstitial voids in LuH₂ are observed, which may explain the formation of Lu₁₀H₂₁ and LuH_3–δN_ε. To provide a basis for comparison, x-ray diffraction patterns and electronic structures of some compounds are also presented.