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

Abstract

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 3 ¯ m 1 ), 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 LuH3–δ N ε . To provide a basis for comparison, x-ray diffraction patterns and electronic structures of some compounds are also presented.