resumo
MXenes are two-dimensional materials that are traditionally composed of transition metal layers intercalated by carbon (carbides) or nitrogen (nitrides) atomic layers. Recently, it was experimentally demonstrated that most, if not all, carbide MXenes synthesized to date are in fact oxycarbides. This includes the titanium carbide (Ti3C2) MXene that is deeply analyzed in this work using a first-principles approach based on density functional theory (DFT). In particular, we studied the stability of the substitutional oxygen defect and clusters thereof in this MXene. In agreement with the experimental suggestions, we found that the oxycarbide forms (Ti3C2-xOx,x is an element of [0, 2]) are structurally and energetically very stable, at least up to 75 % replacement of the carbon atoms with oxygen. If all the carbon is replaced, the surface transitions to a different geometry, in which its atomic layers are aligned in an ABA fashion. Substitutional O clusters in Ti3C2 impose almost no lattice strain, even at high O concentrations, explaining the delay in the identification of oxycarbide MXenes. We found that the Ti3C2-xOx MXenes display metallic behaviour regardless of the oxygen concentration on the carbon layer.
palavras-chave
STABILITY; DEFECTS
categoria
Chemistry; Materials Science; Physics
autores
Gouveia, JD; Gomes, JRB
nossos autores
José Daniel Lago da Silva Neves Gouveia
Investigador Auxiliar
José R. B. Gomes
Investigador PrincipalProjectos
CICECO - Aveiro Institute of Materials (UIDB/50011/2020)
CICECO - Aveiro Institute of Materials (UIDP/50011/2020)
Associated Laboratory CICECO-Aveiro Institute of Materials (LA/P/0006/2020)
MXenes catalysts for the water gas shift reaction (ForTheShift)
Collaboratory for Emerging Technologies, CoLab (EMERGING TECHNOLOGIES)
agradecimentos
This work was developed within the scope of the projects CICECO-Aveiro Institute of Materials, with refs. UIDB/50011/2020, UIDP/50011/2020 and LA/P/0006/2020, and ForTheShift, with ref. 2022.02949.PTDC, financed by national funds through the FCT/MEC (PIDDAC) . We are also thankful to FCT I.P. for the computational resources granted in the framework of project Ref. 2022.15802.CPCA.A2 by the FCT/CPCA/2022/01 Call for Advanced Computing Projects. JDG thanks the Portuguese Foundation for Science and Technology (FCT) through the grants Refs. 2022.00719.CEECIND and 2023.06511.CEECIND, in the scope of the Individual Call to Scientific Employment Stimulus - 5th and 6th Editions.