Metal-oxide interfaces with poor coherency have specific properties comparedto bulk materials and offer broad applications in heterogeneous catalysis, batteries, and electronics. Wagner, Kirkendall, and other researchers have proposed a number of theories to understand the oxidation process based on the ideal atomistic interface model. However, current understanding of the three-dimensional (3D) atomic metal-oxide interfaces remains limited because of their inherent structural complexity and the limitations of conventional two-dimensional imaging techniques. It is, therefore, essential to determine the 3D atomic arrangements and understand the detailed oxidation structure of metal.
On September 2, 2024, the research group led by Prof. Jihan Zhou from the College of Chemistry and Molecular Engineering at Peking University published a research article entitled “Three-dimensional atomic insights into the metal-oxide interface in Zr-ZrO2 nanoparticles” in Nature Communications (https://doi.org/10.1038/s41467-024-52026-w). This study reported the 3D atomic structure of the metal-oxide interface of Zr-ZrO2 determined by atomic resolution electron tomography (AET). The authors quantitatively analyze the atomic concentration and the degree of oxidation, and find that the coherency and translational symmetry of the interfaces are broken. Atoms at the interface exhibit low structural ordering, low coordination, and elongated bond length. Moreover, the authors observe porous structures such as Zr vacancies and nano-pores, and investigate their distribution. These findings provide a clear 3D atomic picture of the metal-oxide interface with direct experimental evidence.
By determining the atomic positions of all Zr atoms in Zr-ZrO2 nanoparticles, this study provides the following understandings of the metal/oxide interface.
(1) The nanoparticle contains unusual FCC Zr as the metal core, and amorphous/crystalline ZrO2 as the shell (Fig. 1).
Fig. 1 Atomic structures of Zr-ZrO2 nanoparticles in 3D.
(2) From the oxide to the metal core, the degree of oxidation gradually decreases, while the packing density of Zr increases. The thickness of the transition interface layer is about 1 nm (Fig. 2).
Fig.2 Atomic concentration and the degree of oxidation of Zr-ZrO2 NP.
(3) Both semi-coherent and incoherent interfaces between Zr and ZrO2 have been identified. At the semi-coherent metal/oxide interface, there is a bidirectional distortion, including bending and twisting. The atomic structure at the incoherent interface exhibits a low degree of order, low coordination number, and longer bond length (Fig. 3).
Fig. 3 3D atomic metal-oxide interfaces.
(4) A variety of voids have been observed and investigated, including Zr vacancies, nano-pores, and the largest pore; the oxidation process is related to the pores (Fig. 4).
Fig. 4 Porous structures during oxidation.
This work could encourage future studies on fundamental problems of oxides, such as interfacial structures in semiconductors and atomic motion during the oxidation process.
The co-first authors are Yao Zhang (a Ph.D. candidate at CCME, Peking University), Dr. Zezhou Li (Ph.D.graduated from CCME, Peking University), and Dr. Xing Tong (an Associate Investigator at Songshan Lake Materials Laboratory). The corresponding authors are Dr. Jihan Zhou and Dr. HaiboKe.
This work was funded by the National Natural Science Foundation of China, the Beijing National Laboratory for Molecular Sciences, and the Guangdong Major Project of Basic and Applied Basic Research, and was supported by the Electron Microscopy Laboratory at Peking University, Bay Area Centre for Electron Microscopy at Songshan Lake Materials Laboratory, Analytical Instrumentation Center at Peking University, and Peking University High Performance Computing Platform.
Link for the article:https://doi.org/10.1038/s41467-024-52026-w
