Density functional theory study of rare earth Y, Ce and La-catalyzed oxidation mechanism of Ta(1 0 0) and Ta(1 1 0) surfaces

Abstract

The density functional theory (DFT) calculations were conducted to study the adsorption and diffusion of oxygen on Ta(100) and Ta(110) with and without the substitution of rare earth (RE, RE = Y, Ce and La) in the surface layer, which aims to reveal the possible RE-catalyzed oxidation mechanism of those two surfaces. The calculated results show that the oxygen atoms are preferentially adsorbed on the hollow site of clean Ta(100) and Ta(110). The RE doping in the subsurface layer weakens the adsorption strength of oxygen on Ta(110), while it has a negligible influence on that on Ta(100). In contrast, the substitution of RE in the surface layer can enhance the adsorption ability of oxygen atom on the two surfaces, which is also proved by the analysis of Bader charge and electron localization function. Additionally, the oxygen atoms are predicted to preferentially occupy the octahedral site in the subsurface of Ta slabs with and without RE doping. The investigations of oxygen diffusion behaviors indicate that the RE, especially for La, doping in the surface layer decrease the energy barrier of oxygen penetration into Ta surface, and thus catalyze the oxidation process of Ta slabs. Those results could help to provide a fundamental basis for comprehending the oxidation mechanism of Ta surface with RE doping.