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, ZrC1-x O x and HfC1-x O 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 TaC1-x O x was not synthesized and NbC1-x O 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. © 2021 The Authors. Published by American Chemical Society.

Citation

Wataru Hayami, Shuai Tang, Ta-Wei Chiu, Jie Tang. Reduction in Work Functions of Transition-Metal Carbides and Oxycarbides upon Oxidation. ACS omega. 2021 Jun 08;6(22):14559-14565

PMID: 34124479

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