Adhesion strength and bonding mechanism of γ-Fe (111)/α-Al2O3 (0001) interfaces with different terminations

Abstract The ideal work of adhesion (Wad), interfacial energy (σ), charge density, charge density difference and partial density of states (PDOS) of the γ-Fe (111)/α-Al2O3 (0001) interface were studied by the first-principles calculations method. The results indicated that three types of interface between Al2O3 (0001) and Fe (111) surface were formed, which are single Al (Al1-terminated), double Al (Al2-terminated) and O (O-terminated). Each type of interface established different stacking sequences, including Hcp-, Hole- and Top-site. The calculation of Wad and σ showed that the stacking sequence of the interface significantly affected the bonding strength and stability. In the optimized stable structure, the stacking sequences of the maximum Wad corresponding to the Al1-, Al2- and O-terminated interfaces are Hcp (0.65 J/m2), Hcp (3.92 J/m2) and Top (9.30 J/m2), respectively. Notably, the maximum Wad for the O-terminated interface is much larger than that for Al1- and Al2-terminated interfaces, implying the O-terminated interface is the largest bonding strength in all interfacial structures. Furthermore, the electronic properties of the interfaces revealed that the order of electron concentration is O-＞Al2-＞Al1-terminated, which vividly reflects the size interaction of the interfaces. Also, the bonds of the Al1-terminated interface are mainly covalent and little metallic bonds, while the Al2-terminated interface performed not only a mixture of metallic and covalent features but also a certain degree of ionic characteristics. Compared to Al1/2-terminated interfaces, the covalent ionic and metallic bonds are formed between Fe and Al/O for the O-terminated interface. Additionally, the type of chemical bond and the number of electron orbital hybrids at the interface are the fundamental reasons that affect the bonding strength of the interface.