Oxygen Chemisorption on the Surface of an In 2 O 3 (011) Nanocrystal
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en Chemisorption on the Surface of an In2O3 (011) Nanocrystal K. S. Kurmangaleeva, *, T. Yu. Mikhailovab, and L. I. Trakhtenberga, c aSemenov
Federal Research Center for Chemical Physics, Russian Academy of Sciences, Moscow, 119991 Russia b Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow, 119991 Russia c Moscow State University, Moscow, 119991 Russia *e-mail: [email protected] Received May 8, 2020; revised June 22, 2020; accepted June 25, 2020
Abstract—Density-functional calculations are used to study the structural and electronic properties of stoichiometric and imperfect In2O3 (011) surfaces. We calculate energies of formation of neutral oxygen vacancies on the surface of an indium oxide nanocrystal and analyze the adsorption of an oxygen atom in its ground (triplet) state on a model imperfect surface having O4 vacancies in different charge states. The results indicate that adsorption on a VO2 + vacancy is the most energetically favorable and that the oxygen atom involved switches from a triplet state to a singlet one. We consider oxygen molecule adsorption from different initial geometric configurations on neutral O1–6 vacancies. Keywords: indium oxide, chemisorption, density functional theory, oxygen, oxygen vacancies, nanocrystal DOI: 10.1134/S0020168520110060
INTRODUCTION Indium oxide-based nanomaterials have a rather wide application area: solar cells [1], conductometric sensors [2, 3], and optoelectronics [4]. The use of materials composed of nanometer elements is known to lead to a marked increase in the role of the specific surface area. Knowledge of surface structure and chemistry is crucial for assessing the influence of these characteristics on the engineering performance of various oxides. Adsorption of atoms and molecules, including those of oxygen, is the first step of many chemical processes. Because of this, to understand such processes it is important to assess energy characteristics of adsorption of particles on stoichiometric or imperfect surfaces. Consider the adsorption of various oxygen species on a nanostructured indium surface, which is of practical interest in many cases. According to X-ray diffraction data, indium oxide nanoparticles have a cubic (bixbyite) structure (sp. gr. Ia 3 , no. 206) [5]. This structure comprises indium atoms in two inequivalent Wyckoff positions, 8b (1/4, 1/4, 1/4) and 24d (u, 0, 1/4), and oxygen atoms in one Wyckoff position, 48e (x, y, z). In accordance with the symmetry elements of space group Ia 3 , there are 80 atoms per unit cell [6]. Simple sections through this structure give a variety of crystallographic planes, which bound grains [7, 8]. These planes have a particular concentration and configuration of surface atoms, and each of
them is characterized by its own features, related to its electronic structure, catalytic properties, and adsorption behavior. According to surface energy calculations [9], the thermodynamic stability of crystallographic planes of indium oxide decreases in the following sequence: (111) >
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