The First Principle Research Of Properities Of TiN And TiC

The transiton metal compounds of the TiN and TiC are generally very hard materials.They have good electrical conductivity,thermal conductivity,high melting point,high pressure and corrosion resistance,which lead to a wide range of applications in the fields of industrial,medical and aerospace.Therefore,it has great significance.of study the such caystal structure in its actual nature in the field of application.In this paper,we use the software of VASP which based on the density functional method of the first principles and study the structural and electronic properties of the compounds of TiN,TiC and TiN_x,TiC_x which includes and doesn't includes the vacance.At first,we study and calculate the structural and electronic properties of TiN and TiC which display face-centered cubic structure of the type of NaCl in the normal pressure.They have benn forecasted transiting to the body-centered cubic structure of the type of CsCl in the high pressure.We take the original cell of TiN and TiC,containing two atoms in each crystal,as studying object.Firstly, we calculate the electronic properties and density of states of the NaCl phase at the pressures of 0GPa,50GPa,100GPa and find the changes less after taking pressure,which shows that the both crystals can endure high pressure.Then we calculated the electronic properties and dendity of states of the CsCl phase at the normal pressure and find it contains more states comparing to the NaCl phases at the around of the Fermi face.Therefore,we conclude it is difficult for energy when forming CsCl phases,simultaneity,we also find that it forms CsCl phase difficulty for the TiN comparing to the TiC.Subsequently,we calculate the erergy-volume(E-V)curve and the enthalpy-pressure(H-P)of the TiN and TiC and find it has less erergys in balance states for the NaCl phase of both crystass comparing to the CsCl phase,which shows the NaCl phase of both crystals have more stable structures than the CsCl phase.Also,we forecast the pressure of the phase transitions from NaCl phase to the CsCl phase according to the H-P curve, which are 170GPa and 300GaPa for TiN and TiC separately.Then,we calculate the bulk modulus and elastic constants of the NaCl phases of the both crystals separately along with the change of the pressure,and find the bulk moduls and elastic constants of the both crystals are enlarging gradually when increasing the pressure,which also conclude the high compression and rigidity of the both TiN and TiC.Secondly,we study the behaviour of the lattice constants,bulk moduli and band structures with vacancy concentration in substoichiometric titanium cabides and nitrides in the NaCl phase by using an eight-atom supercell.We see that the introduction of vacandies in TiN_x and TiC_x decrease the lattice constants and bulk moduli.The observed variation of the lattice constants and bulk modulus as a function of vacancy concentration is founds to be related to the evolution of chemical bonds.We can deduce that these compounds become less rigid with the increase of the vacancy concentration.We report also the variation of the band strcture and DOS with vacncy concentration.There were similarities in the electronic band structure and DOS of these two compounds.The increase of the vacancy concentration is seen by the appearance of vacancy states in the band structure and vacancy peaks in DOS below and around the Fermi level which are due to the d states from broken Ti-C(N)bonds and lead to less hard materials,we consider it as vacancy effects, all of which resulted in crystal callplasing,lattice constants minishing,bulk modulus minishing and caystal stability weakening.