Crystal structure prediction of ReN 2 under high pressure
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SHORT RESEARCH COMMUNICATION
Crystal structure prediction of ReN2 under high pressure H Y Wang1, P Yan1, L Xu1*, D W Zhou2 and D Li3 1
School of Materials Science and Engineering, Henan Polytechnic University, Jiaozuo 454000, China
2
College of Physics and Electronic Engineering, Nanyang Normal University, Nanyang 473061, China 3
Public Experimental Teaching Center, Panzhihua University, Panzhihua 617000, China Received: 18 January 2019 / Accepted: 29 August 2019
Abstract: Three ReN2 phases (Pbcn, C2/m and P4/mbm) are searched to be stable under different pressures by the swarmintelligence-based CALYPSO method. Pressure-induced phase transitions from Pbcn phase to C2/m phase at 68.5 GPa and C2/m phase to P4/mbm phase at 138.8 GPa are firstly observed. The calculated results of density of state show all the three phases are metallic conductor. And elastic constant calculations confirm their mechanical stabilities. The high bulk and shear moduli of C2/m and P4/mbm phases indicate their high hardness. The total and partial electron densities of states and electron localization functions indicate that the covalent bonding of Re–N in ReN2 makes great contributions to the structural stability and high hardness. Keywords: ReN2; Phase transition; High pressure; Structural properties PACS Nos: 62.50.?p; 64.70.Kb; 03.75.Hh
1. Introduction The investigation of new superhard materials is of intense interest to researchers because of their importance in both fundamental sciences and technological applications [1–3]. Due to large number of valence electrons in transition metal and small covalent radii of nitrogen, some transition metal nitrides possess high incompressibility, melting and hardness. Thus, transition metal nitrides are considered as competing candidates for superhard materials. Also, these properties have led to significant fundamental work focused on transition metal nitrides [4–10]. The combination of experiment and first-principles calculation is effective in predicting, testing and confirming the structure of new materials. First-principles calculations have been extensively conducted on transition metal nitrides to explore their structural properties and potential phase transitions [11–19], especially for ReN2. The calculation by Zhao et al. [20] indicates that P42/mnm structure of ReN2 is the most stable at ambient pressures and
*Corresponding author, E-mail: [email protected]; [email protected]
then transforms into Pmmn structure at 76 GPa. Subsequently, Li et al. [21] found that a new ReN2 phase with Pbcn symmetry is more stable than the previously reported P42/mnm and Pmmn structures within the pressure range of 0–100 GPa. And no phase transition is observed at pressures of 0–100 GPa. One should be pointed out that the above researches were calculated by CASTEP code. A different conclusion was obtained by another article [22] conducted by the Vienna ab initio simulation package (VASP), which shows that structural phase transition from Pbcn to P4/mmm phase occurs at 32.7 GPa. And in the above re
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