A first-principle study on the electronic properties of substitutionally Cu (I, II)-doped LiNbO₃

The electronic properties of Cu-doped lithium niobate (LiNbO3) systems are investigated by first-principles calculations. In this work, we focus on substitutionally Cu!Li-doped LiNbO₃ system with cuprous and cupric doping, which corresponds to the Li_5/6Cu_1/6NbO₃ and Li_4/6Cu_1/6NbO₃ [abbreviated as (Li, Cu I)NbO₃ and (Li, Cu II)NbO₃]. The density functional theory (DFT) calculations show that the electronic property of LiNbO₃ is completely different from (Li, Cu I)NbO₃ and (Li, Cu II)NbO₃. The calculated band structure and density of state (DOS) of (Li, Cu I)NbO₃ show a small band gap of 1.34 eV and the top of valance band (VB) is completely composed of a doping energy level originating from Cu 3d filled orbital. However, the calculated band structure and DOS of (Li, Cu II)NbO₃ show a relatively large band gap of 2.22 eV and the top of VB is mainly composed of Cu 3d unfilled orbital and O 2p orbital.