Prediction Of Piezoelectric Properties Of Two-dimensional Nanomaterials Based On First Principle

With the rapid development of two-dimensional nanomaterials represented by graphene,the research and application of two-dimensional nanomaterials in the field of piezoelectrics have received more and more attentions.Single-layer two-dimensional nanomaterials have many unique physical and chemical properties,and have broad and enormous application potential in the fields of micro-nano robots,smart wear,biomimetic materials,et al.Previously,researchers have predicted that many single-layer two-dimensional nanomaterials have excellent piezoelectric properties through first principles theoretical calculation methods,and the piezoelectric properties of some two-dimensional nanomaterials have been experimentally confirmed.However,with the continuous improvement of the level of micro-nano technology and its research.The kind of two-dimensional monolayer nanomaterial is also increasing,there are still some single-layer piezoelectric properties of the current two-dimensional nanomaterial has not been attention and study.Therefore,this paper focuses on the piezoelectric properties of single-layer two-dimensional nanomaterials such as single-layer molybdenum disulfide and Sn Te,Si Te,Ge Te,etc.with similar phosphonene lattice junctions(Puckered structure),and conducts first principles calculation research.The main contents are as follows:Firstly,the development of piezoelectric materials,the rise of two-dimensional materials and the research status of two-dimensional piezoelectric materials are briefly introduced,and the basis and research content of this paper are clarified.Next,we briefly introduced the structural symmetry,elastic constant,piezoelectric constant and other performance parameters of the piezoelectric crystal.Then,the basic theory of first principles,the Berry-phase method and the DFPT calculation method for calculating piezoelectric properties are introduced.For the piezoelectric properties of single-layer molybdenum disulfide(SLMo S₂),considering the various exchange-related functionals commonly used in the literature for the calculation of the electrical properties of SLMo S₂,combined with the energy cutoff of the first principles calculation method and the Kpoint grid,the research is different.The effect of exchange correlation functionals(LDA,PBE,PW91,etc.)on the first-principles calculation results of material properties such as lattice constant,electrical properties,elastic constants,and piezoelectric constants.Comparative calculated and experimental results showed that the calculated LDA Functional bandgap closer to the experimental data,but the calculated elastic constant and piezoelectric constant with the experimental values are quite different;the PBE and PW91functional lattice constant of SLMo S₂.The calculation results of material properties such as Young's modulus and piezoelectric coefficient are not significantly different,and are closer to the experimental results than LDA.For the two-dimensional nano-materials such as SnTe,SiTe and GeTe with puckered structure,based on the PBE exchange correlation functional,the piezoelectric properties are predicted for the first time.The results show that these materials are indirect bandgap semiconductors and have inherent piezoelectric characteristics.Their piezoelectric properties are higher than other two-dimensional nanomaterials such as SLMo S₂.Among them,the piezoelectric constant of Sn Te is the largest in the existing literature,has important potential application value.Finally,the effects of single-atom vacancy defects on the piezoelectric effect of transition metal sulfides(TMDCs)were investigated for the intrinsic lattice defects common to single-layer two-dimensional nanomaterials.The results show that the effect of lattice size increase on the elastic properties and piezoelectric constant of the material is almost negligible,while the single atom vacancy defect can reduce its lattice constant,band gap and Young's modulus,but can increase it's piezoelectric constant.The results of this study can provide a new strategy for the adjustment of piezoelectric properties of two-dimensional nanomaterials.