Crystal structures of transition metal pernitrides predicted from first principles

Rongmei Yu; Ermiao Sun; Liguang Jiao; Yongmao Cai; Hongbo Wang; Yansun Yao

doi:10.1039/c8ra07814a

Crystal structures of transition metal pernitrides predicted from first principles

RSC Adv. 2018 Oct 26;8(64):36412-36421. doi: 10.1039/c8ra07814a.

Authors

Rongmei Yu^{1

2}, Ermiao Sun¹, Liguang Jiao¹, Yongmao Cai³, Hongbo Wang¹, Yansun Yao⁴

Affiliations

¹ State Key Laboratory of Superhard Materials, College of Physics, Jilin University Changchun 130012 P. R. China whb2477@jlu.edu.cn.
² College of Physics and Electronic Engineering, Nanyang Normal University Nanyang 473061 P. R. China.
³ School of Science, Northeast Electric Power University Jilin 132012 P. R. China.
⁴ Department of Physics and Engineering Physics, University of Saskatchewan Saskatoon Saskatchewan S7N 5E2 Canada.

Abstract

We have extensively explored the stable crystal structures of early-transition metal pernitrides (TMN₂, TM = Ti, V, Cr, Mn, Zr, Nb, Mo, Hf, and Ta) at ambient and high pressures using effective CALYPSO global structure search algorithm in combination with first-principles calculations. We identified for the first time the ground-state structures of MnN₂, TaN₂, NbN₂, VN₂, ZrN₂, and HfN₂ pernitrides, and proposed their synthesis pressures. All predicted crystal structures contain encapsulated N₂ dumbbells in which the two N atoms are singly bonded to a [N₂]^4- pernitride unit utilizing the electrons transferred from the transition metals. The strong nature of the single dinitrogen bond and transition metal-nitrogen charge transfer induce extraordinary mechanic properties in the predicted transition metal pernitrides including large bulk modulus and high Vickers hardness. Among the predictions the hardness of MnN₂ is 36.6 GPa, suggesting that it is potentially a hard material. The results obtained in the present study are important to the understanding of structure-property relationships in transition metal pernitrides and will hopefully encourage future synthesis of these technologically important materials.