First-principles Study On Structure Stability,Mechanical And Electrical Properties Of Titanium And Its Hydride Under High Pressure

In recent decades,titanium and its alloys have been widely used in aerospace,deep-sea diving,medicine and other fields due to their high temperature resistance,corrosion resistance and high specific strength.In the extreme physical environment of high temperature and high pressure,titanium reacts with surrounding hydrogen to form titanium hydrides.In addition,studies have shown that high-pressure and hydrogen-rich metals may be potential room temperature semiconductor materials.Therefore,the study of the physical properties of titanium hydrides under high pressure has always been favored by scientists.In this paper,the first-principles calculation based on density functional theory is used to study the structure stability,mechanical properties and electrical properties of TiH_x?x=1,1.5,2?under zero temperature and zero pressure systematically.The results show that?-TiH,?-TiH_1.5.5 and?-TiH₂ with space group P4₂/mmc,P4₂/mcm and I4/mmm have good mechanical and dynamic stability under zero temperature and zero pressure.Their bulk modulus increases with the increase of H component,and the compression resistance is getting stronger.Among them,?-TiH_1.5.5 has the largest Shear modulus and Young's modulus.It can be seen from TDOS and PDOS that these three crystals exhibit metallic properties at zero pressure.The total density is mainly derived from the3d electrons of Ti.In the deep level region below the Fermi level,the s,p,d electrons of Ti and the s electrons of H have strong hybridization.Besides,the influences of pressurization on structural stability,mechanical properties and electrical properties of materials under the same composition are systematically studied.The calculation results show that?-TiH and?-TiH₂ undergo structural phase transition under pressure,and the corresponding phase transformation pressures are 7.5GPa and 67 GPa,respectively.During the pressurization process,their mechanical elastic constants also increase with the increase of pressure.In addition,The anisotropy of TiH and TiH₂ both show different amplitude changes under pressure and tend to be isotropic.The density of states shows that the energy gap appears in the low-energy region of TiH₂with the increase of pressure.?-TiH_1.5.5 is unstable in mechanics when the pressure increased to 60 GPa and it's bulk modulus and toughness increase with the increase of pressure,anisotropy is also more pronounced as pressure increases,but the shear modulus and Young's modulus decrease with the increase of pressure.