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Electronic structure and optical conductivities of 20 MAX-phase compounds

机译:20种MAX相化合物的电子结构和电导率

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The electronic structure and optical conductivities of 20 so-called MAX phases Ti_3AC_2 (A = Al, Si, Ge), Ti_2AC (A = Al, Ga, In, Si, Ge, Sn, P, As, S), Ti_2AlN, M_2A1C (M = V, Nb, Cr), and Ta_(n+1)AlC_n (n = 1 to 4) are studied using the first-principles orthogonalized linear combination of atomic orbitals (OLCAO) method. The calculated results include total and partial density of states, E_ffective charge on each atom, and quantitative bond order values. Also calculated are directionally resolved interband optical conductivities. By analyzing such results regarding these phases (that have different atomic compositions and layered structures) several important features on structural stability and-electrical conductivities are identified and compared with experimental data. We confirm the trend of increasing N(E_f) (total density of states at the Fermi level E_f) as the number of valence electrons of the composing elements increases. The local feature of total density of states (TDOS) near E_f is used to predict structural stability. The calculated E_ffective charge on each atom shows that the M (transition-metal) atoms always lose charge to the X (C or N) atoms, whereas the A-group atoms mostly gain charge but some lose charge. Bond order values are obtained and critically analyzed for all types of interatomic bonds in all the 20 MAX phases.
机译:20个所谓的MAX相Ti_3AC_2(A = Al,Si,Ge),Ti_2AC(A = Al,Ga,In,Si,Ge,Sn,P,As,S),Ti_2AlN,M_2A1C的电子结构和光电导率(M = V,Nb,Cr)和Ta_(n + 1)AlC_n(n = 1至4)使用原子轨道的第一原理正交线性组合(OLCAO)方法进行研究。计算结果包括状态的总密度和部分密度,每个原子上的E_ffective电荷以及定量的键序值。还计算了方向分辨的带间光导率。通过分析有关这些相(具有不同的原子组成和层状结构)的结果,可以确定一些关于结构稳定性和电导率的重要特征并将其与实验数据进行比较。我们确认随着组成元素的价电子数量的增加,N(E_f)(费米能级E_f处的状态总密度)增加的趋势。 E_f附近的状态总密度(TDOS)的局部特征用于预测结构稳定性。计算得出的每个原子上的E情感电荷表明,M(过渡金属)原子始终对X(C或N)原子失去电荷,而A-族原子大部分获得电荷,但有些失去电荷。在所有20个MAX相中,获取并严格分析了所有类型的原子间键的键序值。

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