Pnma-BN: Another Boron Nitride Polymorph with Interesting Physical Properties.
Structural, mechanical, electronic properties, and stability of boron nitride (BN) inPnmastructure were studied using first-principles calculations by Cambridge Serial Total Energy Package (CASTEP) plane-wave code, and the calculations were performed with the local density approximation and generalized gradient approximation in the form of Perdew-Burke-Ernzerhof. This BN, calledPnma-BN, contains four boron atoms and four nitrogen atoms buckled throughsp³-hybridized bonds in an orthorhombic symmetry unit cell with Space group ofPnma.Pnma-BN is energetically stable, mechanically stable, and dynamically stable at ambient pressure and high pressure. The calculated Pugh ratio and Poisson's ratio revealed thatPnma-BN is brittle, andPnma-BN is found to turn brittle to ductile (~94 GPa) in this pressure range. It shows a higher mechanical anisotropy in Poisson's ratio, shear modulus, Young's modulus, and the universal elastic anisotropy indexAU. Band structure calculations indicate thatPnma-BN is an insulator with indirect band gap of 7.18 eV. The most extraordinary thing is that the band gap increases first and then decreases with the increase of pressure from 0 to 60 GPa, and from 60 to 100 GPa, the band gap increases first and then decreases again.
Tianjin Key Laboratory for Civil Aircraft Airworthiness and Maintenance, Civil Aviation University of China, Tianjin 300300, China. zyma@cauc.edu.cn.
Zhenyang
Z
Ma
Tianjin Key Laboratory for Civil Aircraft Airworthiness and Maintenance, Civil Aviation University of China, Tianjin 300300, China. hanzhengcauc@163.com.
Zheng
Z
Han
Tianjin Key Laboratory for Civil Aircraft Airworthiness and Maintenance, Civil Aviation University of China, Tianjin 300300, China. hxliu@126.com.
Xuhong
X
Liu
Tianjin Key Laboratory for Civil Aircraft Airworthiness and Maintenance, Civil Aviation University of China, Tianjin 300300, China. xhyu11987@163.com.
Xinhai
X
Yu
Tianjin Key Laboratory for Civil Aircraft Airworthiness and Maintenance, Civil Aviation University of China, Tianjin 300300, China. dayunwangcauc@163.com.
Dayun
D
Wang
Tianjin Key Laboratory for Civil Aircraft Airworthiness and Maintenance, Civil Aviation University of China, Tianjin 300300, China. ty_cauc@163.com.
Yi
Y
Tian
BN polymorph; anisotropic properties; electronic properties; mechanical properties