Materials Design Of New Me₃AlN Ternary Ceramics

As an important kind of new-type ceramic materials, ternary layered compoundshave attracted material researchers's interests. Ternary layered compounds whosegeneral formula is Me_n+1AX_n (MAX) have the similar structures, where Me is the earlytransition metal, A stands for the same group elements (majority of elements is fromsecond main group and third main group), but X is C or N. Me₃AlN (Me=Ti, Zr, Hf, V,Nb, Ta) ternary ceramics have the silimilar performance with MAX phase. Thesecompounds belong to orthorhombic system and the space-group symbol is Cmcm.These compounds show metal properties, at normal temperature these compounds havegood thermal and electrical conductivity, high elastic modulus and shear modulus.Meanwhile, at high temperature they have good plasticity and can be machined likemetal. The same with other typical ceramics, Me₃AlN compounds have yield strengthand melting point, high thermal-stability, oxidation resistance property.This thesis using the plane waves ultra-soft pseudopotential technique based onthe density functional theory (DFT), the paper calculates some basic properties ofMe₃AlN(Me=Ti,Zr,Hf,V,Nb,Ta), i.e., ground electronic, mechanical properties,thermodynamic performance,mainly including following fields:First of all, the first-principles pseudo-potential plane-waves calculations basedon density functional theroy with GGA approxiation are used. The paper optimizescrystal lattice of Me₃AlN system, gets equilibrium structure of the lowest energy andlattice constants. On basis of optimized structure, the paper calculates energy bandstructure, density of states, electrical conductivity and the bonds mulliken populationof Me₃AlN.Secondly, the paper calculates elastic constants, bulk modulus, shear modulus,poisson ratio, lame constant and so on. According to the calculation results, stability ofcrystal, brittleness and crystal anisotropy have been analyzed.Finally, based on quasi-harmonic Debye model, calculating bulk modulus,thermal expansion coefficient, heat capacity and Grimeisen coefficients are obtainedwith increasing temperature and pressure. Moreover, crystal thermodynamic characterhas been analyzed.