Biaxial strain enhanced piezoelectric properties in monolayer g-${\mathrm{C}}_3{\mathrm{N}}_4$

Abstract

Graphite-like carbon nitride (g-${\mathrm{C}}_3{\mathrm{N}}_4$) is considered as a promising candidate for energy materials. In this work, the biaxial strain (-4\%-4\%) effects on piezoelectric properties of g-${\mathrm{C}}_3{\mathrm{N}}_4$ monolayer are studied by density functional theory (DFT). It is found that the increasing strain can reduce the elastic coefficient $C_{11}$-$C_{12}$, and increases piezoelectric stress coefficient $e_{11}$, which lead to the enhanced piezoelectric strain coefficient $d_{11}$. Compared to unstrained one, strain of 4\% can raise the $d_{11}$ by about 330\%. From -4\% to 4\%, strain can induce the improved ionic contribution to $e_{11}$ of g-${\mathrm{C}}_3{\mathrm{N}}_4$, and almost unchanged electronic contribution, which is different from $\mathrm{Mo}{\mathrm{S}}_2$ monolayer (the enhanced electronic contribution and reduced ionic contribution). To prohibit current leakage, a piezoelectric material should be a semiconductor, and g-${\mathrm{C}}_3{\mathrm{N}}_4$ monolayer is always a semiconductor in considered strain range. Calculated results show that the gap increases from compressive strain to tensile one. At 4\% strain, the first and second valence bands cross, which has important effect on transition dipole moment (TDM). Our works provide a strategy to achieve enhanced piezoelectric effect of g-${\mathrm{C}}_3{\mathrm{N}}_4$ monolayer, which gives a useful guidence for developing efficient energy conversion devices.

6 pages, 4 figures

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