Formation, Electronic Structure, and Defects of Ni Substituted Spinel Cobalt Oxide: a DFT+U Study,The Journal of Physical Chemistry C

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Formation, Electronic Structure, and Defects of Ni Substituted Spinel Cobalt Oxide: a DFT+U Study
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2016-06-28 00:00:00 , DOI: 10.1021/acs.jpcc.6b03096
Xiao Shi ₁ , Steven L. Bernasek _{1,

2} , Annabella Selloni ₁

Affiliation

Nickel substituted spinel cobalt oxide is a promising technological material with complex electronic and magnetic structures. Understanding these structures is important for improving the material’s performance in various applications. We have carried out first-principles calculations on the formation, electronic properties, and defects of bulk NiCo₂O₄ using density functional theory (DFT) with on-site Hubbard U terms on the transition metal d states. Analysis of the electronic structure of Ni_xCo_3-xO₄ as a function of x = 0–1 shows that Ni acts as a p-type dopant in Co₃O₄, gradually transforming the minority spin channel from insulating to conducting. As a result, the inverse spinel NiCo₂O₄ (NCO) is found to have a ferrimagnetic half-metallic ground state with fractional valence on Ni and Co cations at tetrahedral sites (Td), in agreement with experimental observations. Projected densities of states confirm that the states around the Fermi energy originate from Ni and Co(Td) 3d states hybridized with oxygen 2p orbitals. The influence of two common defects, Ni ↔ Co(Td) exchanges and oxygen vacancies, on the structural and electronic properties has been also investigated. Our results are consistent with the experimental observation that intermediate structures between inverse spinel and normal spinel occur frequently in NCO. Oxygen vacancies are predicted to occur more frequently at sites coordinated to a larger number of Ni ions and found to have only minor effects on the conductivity and magnetic structure.

中文翻译：

Ni取代的尖晶石型钴氧化物的形成，电子结构和缺陷：DFT + U研究

镍取代的尖晶石型氧化钴是一种有前途的技术材料，具有复杂的电子和磁性结构。了解这些结构对于提高材料在各种应用中的性能非常重要。我们使用密度泛函理论（DFT）在过渡金属d态上具有现场Hubbard U项，对块状NiCo ₂ O ₄的形成，电子性质和缺陷进行了第一性原理计算。根据x = 0–1对Ni _x Co _{3- x} O ₄的电子结构的分析表明，Ni在Co ₃ O _4中充当p型掺杂剂，逐步将少数自旋通道从绝缘转变为导电。结果，反尖晶石NiCo ₂ O ₄（NCO）具有亚铁磁性的半金属基态，在四面体位点（Td）的Ni和Co阳离子上具有分数价，与实验观察一致。预计的状态密度确认费米能量周围的状态源自与氧2p轨道杂化的Ni和Co（Td）3d状态。还研究了两种常见缺陷Ni↔Co（Td）交换和氧空位对结构和电子性能的影响。我们的结果与实验观察一致，即反尖晶石和正尖晶石之间的中间结构在NCO中频繁发生。预计氧空位会在与大量Ni离子配位的位置上更频繁地发生，并且发现它们对电导率和磁性结构的影响很小。

更新日期：2016-06-28

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