过渡金属单硼化物TMB的第一性原理研究

First-principles Study of Transition Metal Monoboride TMB

基于密度泛函理论平面赝势波法的第一性原理计算,研究过渡金属单硼化物TMB(以3d系列中的TiB、VB和CrB;4d系列中的ZrB、NbB和MoB;5d系列中的HfB、TaB和WB为例)的热力学稳定性、力学性质和微观机制.发现过渡金属单硼化物的热力学稳定与硬度异常的规律.当价电子浓度为8 e·(f.u.)-1时,热力学最稳定,且硬度最高.计算TMB的电子结构,发现TMB的价电子浓度为8 e·(f.u.)-1时,pd共价键合,有效阻碍了金属双层之间的位错滑动,防止剪切变形,致使其具有高硬度.

We study thermodynamic stability,mechanical properties,and microscopic mechanisms of transition metal monoboride TMB(take TiB,VB and CrB in 3 d series;ZrB,NbB and MoB in 4 d series;HfB,TaB and WB in 5 d series as examples)by first-principles calculations based on density functional theory and plane pseudopotential wave method.We found thermodynamic stability and hardness anomalies of transition metal monoborides.In particular,as valence electron concentration is 8 e·(f.u.)-1,thermodynamic stability is the most stable and hardness is the highest.To reveal its mechanism,we calculated electronic structure of TMB.As valence electron concentration of TMB is at 8 e·(f.u.)-1,covalent bonding of pd blocked effectively dislocation slipping between metal bilayers,prevented shear deformation,and resulted in high hardness.These discoveries may help new superhard material designs.