First-principle Study Of The Physical And Mechanical Properties Of A Typical Two-dimensional MXene System

Since the discovery of two-dimensional MXene,it has received extensive attention due to its similarity to the structure of graphene.With the continuous in-depth research on its properties and potential applications,some two-dimensional MXenes have been proven to have excellent mechanical and electrical properties and have the potential as electrode materials.However,there is still a small part of the two-dimensional MXene performance that has not been fully studied.In addition,studies have found that it is possible to change the surface functional groups of two-dimensional MXene and apply an external field to adjust its performance,but there is still a lack of research on its mechanical properties.Therefore,this paper uses first principle to select a suitable two-dimensional MXene to study its performance.Firstly,the structure,electronic properties and mechanical properties of two-dimensional Nb₃C₂and Nb₃C₂T₂（T=O,F,OH）are systematically studied.It was found that the capping of the three functional groups has a significant effect on the bond length within the structure,and the reason for the bond length change is explained in the paper by the electron transfer between atoms.After studying the electronic structure,it is found that the two-dimensional Nb₃C₂is still a conductor after being terminated by functional groups,but the conductivity has changed.In addition,through the pdos diagram,we can understand the contribution of the state density of each orbital at the Fermi energy level in different structures.By stretching the structures,O functional groups were found to significantly enhance the mechanical properties of two-dimensional Nb₃C₂,including tensile resistance,strength limit and Young’s modulus.And by studying the bond length changes of each structure during the stretching process,we have explained in depth how the functional groups affect the mechanical properties of two-dimensional Nb₃C₂.Next,the composition of the surface functional groups and the effect of the arrangement on their electronic structure and mechanical properties were investigated by selecting two-dimensional Ti₃C₂suitable for the construction of the Janus model.The study of the electronic structure found that the coupling degree between the 3d orbital of Ti atom and the 2p orbital of C atom increases as the proportion of F atoms in the surface functional groups increases,but the energy range for hybridization decreases accordingly.In addition,the degree of coupling between the orbitals decreases as the symmetry of the surface functional groups decreases.In terms of mechanical properties,the strength limit of the system increases as the proportion of O atoms in the surface functional groups increases,while the tensile strength increases as the proportion of F atoms increases.In addition,the arrangement of surface functional groups will also affect it.When the ratio of functional groups is the same,the strength limit and tensile capacity of the system decrease with the decrease of symmetry.The reasons for the variation in mechanical properties were also explained by the analysis of bond lengths.Finally,the effect of external field on the electronic properties of two-dimensional Nb₃C₂and its three functionalized structures was investigated.The study found that the metal properties of Nb₃C₂and Nb₃C₂T₂（T=O,F,OH）are very stable under the action of electric field in the positive and negative directions and tensile strain,and there is no transition from conductor to semiconductor.But under the action of electric field and tensile strain,its conductivity will change.