Singh Vijay, Major Dan Thomas
Department of Chemistry, Lise Meitner-Minerva Center of Computational Quantum Chemistry, and Institute for Nanotechnology and Advanced Materials, Bar-Ilan University , Ramat-Gan 52900, Israel.
Inorg Chem. 2016 Apr 4;55(7):3307-15. doi: 10.1021/acs.inorgchem.5b02426. Epub 2016 Mar 24.
The mixed valence cobalt oxide, Co3O4, is a potential candidate as a photovoltaic (PV) material, which also exhibits intriguing chemical and catalytic properties. Here, we present a comparative study of the electronic, magnetic, and chemical bonding properties of mixed valence Co3O4 (i.e., Co(2+/3+)) with the related single valence CoO (i.e., Co(2+)) and Co2O3 (i.e., Co(3+)) oxides using density functional theory (DFT). We have employed a range of theoretical methods, including pure DFT, DFT+U, and a range-separated exchange-correlation functional (HSE06). We compare the electronic structure and band gap of the oxide materials, with available photoemission spectroscopy and optical band gaps. Our calculations suggest that the bonding between Co(3+) and O(2-) ions in Co2O3 and Co3O4 and Co(2+) and O(2-) ions in CoO and Co3O4 are rather different. We find that Co2O3 and Co3O4 are weakly correlated materials, whereas CoO is a strongly correlated material. Furthermore, our computed one-electron energy level diagrams reveal that strong Co-O antibonding states are present at the top of the valence band for all the cobalt oxides, hinting at a defect tolerant capacity in these materials. These results, which give a detailed picture of the chemical bonding in related single and mixed valence cobalt oxides, may serve as a guide to enhance the PV or photoelectrochemical activity of Co3O4, by reducing its internal defect states or changing its electronic structure by doping or alloying with suitable elements.
混合价态的氧化钴Co3O4是一种有潜力的光伏（PV）材料候选物，它还展现出有趣的化学和催化性质。在此，我们使用密度泛函理论（DFT）对混合价态的Co3O4（即Co(2+/3+)）与相关的单价态CoO（即Co(2+)）和Co2O3（即Co(3+)）氧化物的电子、磁性和化学键合性质进行了比较研究。我们采用了一系列理论方法，包括纯DFT、DFT+U以及范围分离的交换关联泛函（HSE06）。我们将氧化物材料的电子结构和带隙与现有的光电子能谱和光学带隙进行了比较。我们的计算表明，Co2O3和Co3O4中Co(3+)与O(2-)离子之间的键合以及CoO和Co3O4中Co(2+)与O(2-)离子之间的键合有很大不同。我们发现Co2O3和Co3O4是弱关联材料，而CoO是强关联材料。此外，我们计算得到的单电子能级图表明，所有钴氧化物的价带顶部都存在强Co-O反键态，这暗示了这些材料具有缺陷容忍能力。这些结果详细描绘了相关单价态和混合价态钴氧化物中的化学键合情况，可作为通过减少其内部缺陷态或通过与合适元素掺杂或合金化来改变其电子结构，从而提高Co3O4的光伏或光电化学活性的指导。
