Structural Prediction And Proterties Of Titanium Nitride Under High Pressure

The existing state of material becomes rich and varied due to high pressure,and the novel physical and chemical properties of materials can be found,which greatly broadens the direction and dimensions of material research.With the pressure increasing,interatomic distance of matter will be decreased,leading to structural phase transitions.Titanium nitride(Ti N)is one of representative transition metal mononitrides,which has excellent properties such as very high melting temperature,excellent corrosion resistance,and extreme hardness.Hence,it is widely used as hard coatings and resistant coatings under extreme conditions.Here the physics properties,including structural phase transition,elastic,and thermodynamic properties of Ti N at pressures have been studied by combining first principles calculations and particle-swarm optimization algorithm.Our results are presented as follows:(i)Three high-pressure phases of Ti N and their transition sequence are identified as B1-> P63/mmc-> B2.The phase transition from the B1 phase to the P63/mmc phase takes place at the pressure of 270 GPa,and in turn the second transition from the P63/mmc phase to B2 phase occurs at the pressure of 347 GPa.(ii)The calculated phonons reveal no negative frequencies for the three structures at high pressures,indicating that they are dynamical stable.(iii)The elastic and thermodynamic properties for the three phases have been calculated,the elastic properties show that both of the B1 and P63/mmc phases are close to be isotropic,while the B2 phase is found to be quite anisotropic.Both of the B1 and P63/mmc belong to brittle materials,while the B2 phase is a ductile material.The chemical bonds for the B1 and P63/mmc phases are stronger than B2,thus show larger Debye temperature than B2.Our research provides a valuable theoretical basis for the synthesis and application...