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

The electronic properties of Cu-doped lithium niobate (LiNbO 3 ) systems are investigated by first-principles calculations. In this work, we focus on substitutionally Cu[Formula: see text]Li-doped LiNbO 3 system with cuprous and cupric doping, which corresponds to the Li[Formula: see text]Cu[Formula: see text]NbO 3 and Li[Formula: see text]Cu[Formula: see text]NbO 3 [abbreviated as (Li, Cu I)NbO 3 and (Li, Cu II)NbO 3 ]. The density functional theory (DFT) calculations show that the electronic property of LiNbO 3 is completely different from (Li, Cu I)NbO 3 and (Li, Cu II)NbO 3 . The calculated band structure and density of state (DOS) of (Li, Cu I)NbO 3 show a small band gap of 1.34[Formula: see text]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)NbO 3 show a relatively large band gap of 2.22[Formula: see text]eV and the top of VB is mainly composed of Cu 3d unfilled orbital and O 2p orbital.