First-principles Study On The Structure And Properties Of Layered Ceramics In Zr-Al-C System

MAX or MAX-like layered materials exhibit excellent metal-ceramic dual properties and are used as high temperature structural materials.Among them,Zr-Al-C nano-layered material ceramics exhibit excellent performance and have received extensive attention in recent years.In this paper,based on the application of high temperature thermal structural materials,we selected the 211 phase(2nAlC),312 phase(2dAlC2)in Zr-Al-C system of MAX phase and(ZrC)11AL3C2,(ZrC)nAl4C3-(n=1,2,3)MAX phase-like system as research objects.The first-principles plane wave pseudopotential method is used to calculate the structure,elasticity and electronic properties of materials under high pressure,and we choose the 211 phase and 312 phase as example,compared the difference between M2AlC(M=Zr,Ti,Hf)and M3AIC2(M=Zr,Ti).For the more complex(ZrC)nAlbC2(n=2,3,4)and(ZrC)nAl4C3(n=1,2,3)systems,their regularity is explored from the aspects of crystal structure,elastic properties and electronic properties.The main findings are as follows:1.optimizated the structural of Zr2AlC,Zr3AlC2,M2AIC(M=Zr,Ti,Hf)and M3AlC2(M=Zr,Ti)under high pressure,obtaining lattice constant and cell volume,and calculating the elastic properties,calculation results is in good agreement with the experimental data.It is found that these crystals can exist stably and have anisotropy within the pressure range;as for the more complex structure 312 phase,the lattice parameters,elastic constant,elastic modulus and density of states are more afrected by pressure under the influence of pressure.211 phase M2AlC(M=Zr,Ti,Hf)and 312 phase M3AlC2(M=Zr,Ti)all satisfy the minimum influence of pressure when M=Zr.2.Six crystals Zr2Al3C4,Zr3Al3C5,Zr4Al3C6 and ZrAl4C4,ZnAl4C5 and Zr3Al4C6 were studied respectively.It is found that these six crystals can be divided into(ZrC) nAl3C2(n=2,3,4)and(ZrC)(?)nAl4C5(n=2,3)according to the constituent units.In this paper,the lattice constants and the cell volume are optimized for these six crystal structures,and the elastic properties are calculated.The calculated results agree well with the experimental data.It is found that the relationship between the moduli B,the shear modulus G and the Young’s modulus E satisfies:Al4C3<ZrAl4C4<Zr2Al4Cs<Zr3Al4C6<Zr2Al3C4<Zr3Al3C5<Zr4Al3C6<ZrC3.From the state density and layout analysis,Zr2AlC、Zr3AlC2、ZnAl3C4、 ZnAl3C5、Zr4Al3C6,ZrAl4C4、Zr2Al4C5 and ZrAl4C6 are all metallic,covalent and ionic.