过渡金属碳化物和氧碳化物氧化功函数的降低,ACS Omega

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过渡金属碳化物和氧碳化物氧化功函数的降低
ACS Omega ( IF 3.7 ) Pub Date : 2021-05-27 , DOI: 10.1021/acsomega.1c01671
Wataru Hayami ₁ , Shuai Tang ₂ , Ta-Wei Chiu ₂ , Jie Tang ₂

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在此，通过第一性原理计算研究了第 4 族和第 5 族过渡金属（Ti、Zr、Hf、V、Nb 和 Ta）碳化物和过渡金属碳氧化物（TMCO）的功函数，以研究它们作为电子的潜在应用。发射器。随着碳原子被氧取代，两组的功函数均下降，第 4 组的还原量大于第 5 组。尤其是 ZrC _{1– x} O _x和 HfC _{1– x} O _x ( x ≥ 0.25) 表现出小于 3 eV 的功函数，与 LaB _{6 的}功函数相当- 和 ZrO 涂层钨。功函数的减少可以用电子态密度的刚带模型来解释。价电子的增加增加了费米能量，而它对真空势的影响较小，导致功函数降低。声子色散曲线表明，NaCl 型第 5 组 TMCO 不如第 4 组 TMCO 稳定。这符合该实验发现的TaC _{1- X} ø _X没有被合成和NbC的_{1- X} ø _X只为更小的值来合成X（即，X< 0.28)。从功函数和结构稳定性的角度来看，第 4 族（Ti、Zr 和 Hf）TMCO 比第 5 族（V、Nb 和 Ta）TMCO 作为电子发射体表现出更好的应用潜力。

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Reduction in Work Functions of Transition-Metal Carbides and Oxycarbides upon Oxidation

Herein, the work functions of group 4 and group 5 transition-metal (Ti, Zr, Hf, V, Nb, and Ta) carbides and transition-metal oxycarbides (TMCOs) were investigated by first-principles calculations for their potential application as electron emitters. The work functions of both groups decreased as the substitution of carbon atoms with oxygen proceeded, and the reduction in group 4 was more than that of group 5. In particular, ZrC_1–xO_x and HfC_1–xO_x (x ≥ 0.25) exhibited work functions of less than 3 eV, which were comparable with those of LaB₆- and ZrO-coated tungsten. The reduction in the work functions could be explained by the rigid-band model of the electronic density of states. The increase in valence electrons increased the Fermi energy, while it demonstrated a less significant influence on the vacuum potential, resulting in a reduction in the work functions. The phonon dispersion curves indicated that the NaCl-type group 5 TMCOs were less stable than the group 4 TMCOs. This agrees with the experimental findings that TaC_1–xO_x was not synthesized and NbC_1–xO_x was synthesized only for smaller values of x (i.e., x < 0.28). From the viewpoints of the work functions and structural stabilities, group 4 (Ti, Zr, and Hf) TMCOs exhibit better potential for application as electron emitters than group 5 (V, Nb, and Ta) TMCOs.

更新日期：2021-06-08

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