First-Principles Study of CuGaO2 Polymorphs: Delafossite α-CuGaO2 and Wurtzite β-CuGaO2

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• 作者：Issei Suzuki ; Hiraku Nagatani ; Masao Kita ; Yuki Iguchi ; Chiyuki Sato ; Hiroshi Yanagi ; Naoki Ohashi ; Takahisa Omata
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：August 1, 2016
• 年：2016
• 卷：55
• 期：15
• 页码：7610-7616
• 全文大小：413K
• 年卷期：0
• ISSN：1520-510X

文摘

The electronic structures of delafossite α-CuGaO₂ and wurtzite β-CuGaO₂ were calculated based on density functional theory using the local density approximation functional including the Hubbard correction (LDA+U). The differences in the electronic structure and physical properties between the two polymorphs were investigated in terms of their crystal structures. Three major structural features were found to influence the electronic structure. The first feature is the atomic arrangements of cations. In the conduction band of α-CuGaO₂ with a layered structure of Cu₂O and Ga₂O₃, Cu and Ga states do not mix well; the lower part of the conduction band mainly consists of Cu 4s and 4p states, and the upper part consists of Ga 4s and 4p states. By contrast, in β-CuGaO₂, which is composed of CuO₄ and GaO₄ tetrahedra, Cu and Ga states are well-mixed. The second feature is the coordination environment of Cu atoms; the breaking of degeneracy of Cu 3d orbitals is determined by the crystal field. Dispersion of the Cu 3d valence band of β-CuGaO₂, in which Cu atoms are tetrahedrally coordinated to oxygen atoms, is smaller than those in α-CuGaO₂, in which Cu atoms are linearly coordinated to oxygen atoms; this results in a larger absorption coefficient and larger hole effective mass in β-CuGaO₂ than in α-CuGaO₂. The interatomic distance between Cu atoms—the third feature—also influences the dispersion of the Cu 3d valence band (i.e., the effective hole mass); the effective hole mass decreases with decreasing interatomic distance between Cu atoms in each structure. The results obtained are valuable for understanding the physical properties of oxide semiconductors containing monovalent copper and silver.