Lu–H–N Phase Diagram from First-Principles Calculations
Fankai Xie, Tenglong Lu, Ze Yu, Yaxian Wang, Zongguo Wang, Sheng Meng, Miao Liu
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 Lu 20 H 2 N 17 ( C 2/ m ) and Lu 2 H 2 N ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>P</mml:mi> <mml:mover accent="true"> <mml:mn>3</mml:mn> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>m</mml:mi> <mml:mn>1</mml:mn> </mml:mrow> </mml:math> ), 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 LuN 9 and Lu 10 H 21 . Additionally, interstitial voids in LuH 2 are observed, which may explain the formation of Lu 10 H 21 and LuH 3– δ N ε . To provide a basis for comparison, x-ray diffraction patterns and electronic structures of some compounds are also presented.