Cl原子在γ-TiAl(111)表面吸附的第一性原理研究

First-principles study on chemisorption of Cl on γ-TiAl(111) surface

基于密度泛函理论,在广义梯度近似下研究了Cl在γ-TiAl(111)表面的吸附.计算结果表明:γ-TiAl(111)表面的面心立方位置(fcc)和六角密排位置(hcp)为Cl吸附的稳定位置,当覆盖度Θ小于一个单层(ML)时,Cl原子倾向于吸附在γ-TiAl(111)表面近邻为多Ti的位置.电子结构分析发现,Cl原子同表面金属原子形成较强的离子键,并且成键具有一定的方向性.当Cl原子和O原子共同在γ-TiAl(111)表面吸附时,二者都趋于优先占据表面fcc和hcp位置,从而形成吸附竞争;另外,Cl原子的吸附将升高平均每个O原子的吸附能,从而减弱O原子与表面金属原子的结合,这可能是实验中氯化处理能使γ-TiAl抗氧化能力提高的原因之一。

The chemisorption of Cl atoms on the γ-TiAl（111） surface is investigated by density functional theory.The calculated results show that the more stable sites for Cl atoms adsorption are the surface face-centred cubic（fcc） sites and the surface hexagonal close-packed（hcp） sites.When the coverage of Cl is less than 1 monolayer（ML）,Cl atoms prefer the adsorption site with more Ti atoms as its nearest neighbors on the surface layer.From the analysis of the electronic structures,it can be found that the bonds formed by Cl and metal atoms are mainly ionic and directional.When Cl and O atoms are co-adsorbed on γ-TiAl（111） surface,both of them prefer the fcc and hcp sites.As a result,there is a competition between them.Furthermore,the adsorption energy per oxygen atom is increased by the adsorption of Cl atoms,which indicates that interactions between oxgen and metal atoms are weakened by the adsorption of Cl atoms on γTiAl（111） surface.This may be one of the reasons why the oxidation resistance of γ-TiAl can be improved by chlorine treatment.