Dependence of elastic stiffness on electronic band structure of nanolaminate M2AlC (M=Ti,V,Nb, and Cr) ceramics
Dependence of elastic stiffness on electronic band structure of nanolaminate M2AlC (M=Ti,V,Nb, and Cr) ceramics
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DOI：
10.1103/physrevb.69.214111
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发表时间：
2004-06
影响因子：
3.7
通讯作者：
Jingyang Wang;Yanchun Zhou
中科院分区：
文献类型：
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作者：
Jingyang Wang;Yanchun Zhou
采用从头算赝势总能量法研究了纳米层合M2AlC （M=Ti，V,Nb, Cr）陶瓷的弹性刚度和电子能带结构。讨论了弹性刚度与价电子浓度的关系。结果表明：随着VEC的增加，M2AlC的体模量和剪切模量单调增加；剪切模量c（44）在VEC为8.4 ~ 8.6时达到最大值，其本身代表纯剪切形状变化，与硬度有直接关系。这说明随着VEC的变化，M2AlC的体模量、剪切模量和硬度有不同的变化趋势。此外，在电子能带结构分析方面，弹性刚度的趋势得到了很好的解释，例如，M2AlC在费米能级附近的价电子的占据。我们发现体积模量和剪切模量的增加源于附加的价电子填充态，包括Md-Alp共价键和金属间的t（2g）和e(g)轨道。对于c(44)，强化M-Al - pd共价键有效地提高了抗剪切能力，而过多占据dd轨道则产生了负贡献。c（44）的最大值归因于Md-Alp键态的完全填充。
We investigate the elastic stiffness and electronic band structure of nanolaminate M2AlC (M=Ti,V,Nb, and Cr) ceramics by using the ab initio pseudopotential total energy method. The relationship between elastic stiffness and valence electron concentration (VEC) is discussed. The results show that the bulk and shear moduli enhance monotonously as VEC increases in M2AlC. The shear modulus c(44), which by itself represents a pure shear shape change and is directly related to hardness, reaches its maximum when the VEC is in the range of 8.4-8.6. This implies that the bulk modulus, shear modulus, and hardness vary in different trends when the VEC changes in M2AlC. Furthermore, trends in the elastic stiffness are well explained in terms of electronic band structure analysis, e.g., occupation of valence electrons in states near the Fermi level of M2AlC. We show that increments of bulk and shear moduli originate from additional valence electrons filling states involving Md-Alp covalent bonding and metal-to-metal t(2g) and e(g) orbitals. For the case of c(44), strengthening the M-Al pd covalent bonds effectively enhances the shear resistance and excessive occupation of dd orbitals gives rise to a negative contribution. The maximum of c(44) is attributed to the complete filling of the Md-Alp bonding states.