Issue 
EPL
Volume 132, Number 5, December 2020



Article Number  57002  
Number of page(s)  6  
Section  Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties  
DOI  https://doi.org/10.1209/02955075/132/57002  
Published online  30 December 2020 
Intrinsic piezoelectricity in monolayer MSi_{2}N_{4} (M = Mo, W, Cr, Ti, Zr and Hf)
^{1} School of Electronic Engineering, Xi'an University of Posts and Telecommunications  Xi'an 710121, China
^{2} Key Laboratary of Advanced Semiconductor Devices and Materials, Xi'an University of Posts and Telecommunications  Xi'an 710121, China
^{3} Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Science 110016 Shenyang, Liaoning, China
^{4} School of Materials Science and Engineering, University of Science and Technology of China Shenyang 110016, China
^{(a)} sandongyuwang@163.com
Received: 22 September 2020
Accepted: 1 December 2020
Motived by experimentally synthesized $\mathrm{MoSi}_{2}\mathrm{N}_{4}$ (Hong Y. L. et al., Science, 369 (2020) 670), the intrinsic piezoelectricity in monolayer $\mathrm{MSi}_{2}\mathrm{N}_{4}$ ($\mathrm{M}=\mathrm{Mo}$ , W, Cr, Ti, Zr and Hf) are studied by density functional theory (DFT). Among the six monolayers, $\mathrm{CrSi}_{2}\mathrm{N}_{4}$ has the best piezoelectric strain coefficient d_{11} of 1.24 pm/V, and the second is 1.15 pm/V for $\mathrm{MoSi}_{2}\mathrm{N}_{4}$ . Taking $\mathrm{MoSi}_{2}\mathrm{N}_{4}$ as a example, strain engineering is applied to improve d_{11}. It is found that tensile biaxial strain can enhance d_{11} of $\mathrm{MoSi}_{2}\mathrm{N}_{4}$ , and the d_{11} at 4% strain can improve by 107% with respect to the unstrained one. By replacing the N by P or As in $\mathrm{MoSi}_{2}\mathrm{N}_{4}$ , the d_{11} can be raised substantially. For $\mathrm{MoSi}_2\mathrm{P}_{4}$ and $\mathrm{MoSi}_{2}\mathrm{As}_{4}$ , the d_{11} is as high as 4.93 pm/V and 6.23 pm/V, which is mainly due to smaller $C_{11}C_{12}$ and very small minus or positive ionic contribution to piezoelectric stress coefficient e_{11} with respect to $\mathrm{MoSi}_{2}\mathrm{N}_{4}$ . The discovery of this piezoelectricity in monolayer $\mathrm{MSi}_{2}\mathrm{N}_{4}$ enables active sensing, actuating and new electronic components for nanoscale devices, and is recommended for experimental exploration.
PACS: 71.20.b – Electron density of states and band structure of crystalline solids / 77.65.j – Piezoelectricity and electromechanical effects
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