Kenmoe Stephane, Douma Dick Hartmann, Raji Abdulrafiu Tunde, M'Passi-Mabiala Bernard, Götsch Thomas, Girgsdies Frank, Knop-Gericke Axel, Schlögl Robert, Spohr Eckhard
Department of Chemistry, University of Duisburg-Essen, Universitätsstr. 2, 45141 Essen, Germany.
Groupe de Simulations Numériques en Magnétisme et Catalyse, Faculté des Sciences et Techniques, Université Marien Ngouabi, Brazzaville B.P. 69, Congo.
Nanomaterials (Basel). 2022 Mar 10;12(6):921. doi: 10.3390/nano12060921.
We combine theoretical and experimental X-ray absorption near-edge spectroscopy (XANES) to probe the local environment around cationic sites of bulk spinel cobalt tetraoxide (Co3O4). Specifically, we analyse the oxygen -edge spectrum. We find an excellent agreement between our calculated spectra based on the density functional theory and the projector augmented wave method, previous calculations as well as with the experiment. The oxygen -edge spectrum shows a strong pre-edge peak which can be ascribed to dipole transitions from O 1s to O 2p states hybridized with the unoccupied 3d states of cobalt atoms. Also, since Co3O4 contains two types of Co atoms, i.e., Co3+ and Co2+, we find that contribution of Co2+ ions to the pre-edge peak is solely due to single spin-polarized t2g orbitals (dxz, dyz, and dxy) while that of Co3+ ions is due to spin-up and spin-down polarized eg orbitals (dx2-y2 and dz2). Furthermore, we deduce the magnetic moments on the Co3+ and Co2+ to be zero and 3.00 μB respectively. This is consistent with an earlier experimental study which found that the magnetic structure of Co3O4 consists of antiferromagnetically ordered Co2+ spins, each of which is surrounded by four nearest neighbours of oppositely directed spins.
我们结合理论和实验X射线吸收近边光谱（XANES）来探测块状尖晶石四氧化钴（Co3O4）阳离子位点周围的局部环境。具体而言，我们分析了氧边光谱。我们发现基于密度泛函理论和投影增强波方法计算得到的光谱、先前的计算结果以及实验结果之间具有很好的一致性。氧边光谱显示出一个强烈的预边峰，这可归因于从O 1s到与钴原子未占据的3d态杂化的O 2p态的偶极跃迁。此外，由于Co3O4包含两种类型的Co原子，即Co3 +和Co2 +，我们发现Co2 +离子对预边峰的贡献仅源于单自旋极化的t2g轨道（dxz、dyz和dxy），而Co3 +离子的贡献则源于自旋向上和自旋向下极化的eg轨道（dx2 - y2和dz2）。此外，我们推断Co3 +和Co2 +上的磁矩分别为零和3.00 μB。这与早期的一项实验研究一致，该研究发现Co3O4的磁结构由反铁磁有序的Co2 +自旋组成，每个Co2 +自旋都被四个自旋方向相反的最近邻包围。
