过渡金属Tc及其氮化物TcN,TcN_2,TcN_3与TcN_4低压缩性的第一性原理计算研究

First-principles study of low-compressibility of transition-metal Tc and its nitrides TcN,TcN_2,TcN_3 and TcN_4

采用基于密度泛函理论的第一性原理计算方法研究了Tc及其氮化物的弹性性质、电子结构、原子布局数等,并分析和计算了它的氮化物的理论硬度.结果表明随着Tc中氮的掺入量的渐增,出现层状结构,它们的弹性模量并非单调增加,其中TcN的体弹模量最大而剪切模量最小;层状结构的TcN3的剪切模量最大而体弹模量最小,TcN4的理论计算硬度最大.说明在Tc的氮化物中,其体弹模量与材料的晶体结构、平均每个原子上的电荷密度和材料的质量密度有关;化学键的共价性结构和氮元素的含量对理论计算硬度有正作用;而剪切模量的极大值则与其层状结构及体系中一定量的方向基本一致的N—N键相关.

Tc and its nitrides TcN, TcN2, TcN3 and TcN4 are studied using the projector augmented wave method based on the density functional theory. The elastic properties, electronic structure and atomic populations, theoretical hardness of Tc nitrides are calculated and analyzed. The calculation results show that with increasing N content by incorporated into transition-metal Tc, the solid structures of the material change into laminar, and its elastic moduli do not monotonically increase. It reveals that TcN with solid structure has the largest bulk modulus and the smallest shear modulus, while TcN3 with layered structure has the largest shear modulus and the smallest bulk modulus, and TcN4 is found to have the largest theoretical hardness by means of chemical bonding analysis. It can be seen that the bulk modulus depends mainly on electrons per atomic volume and mass density, while covalent structure of chemical bonding and N content make more contribution to theoretical hardness, and appropriate content N--N covalent bonding in the same direction tends to increase the shear modulus of nitrides.