Interaction between Bi Dopants and Intrinsic Defects in LiNbO₃ from Local and Hybrid Density Functional Theory...

The interactions between Bi dopants including Bi-substituting Li (Bi_Li) and Bi-substituting Nb (Bi_Nb) and the intrinsic antisite defects (Nb_Li) and Li vacancies (V_Li) in LiNbO₃ are investigated using local and hybrid density functional theories. Three charge-compensated defect clusters, Bi_Li⁴⁺ + Nb_Li⁴⁺ + 8V_Li^-, Bi_Li⁴⁺ + 4V_Li^-, and Bi_Li⁴⁺ + Bi_Nb⁰ + 4V_Li^-, are modeled in this work to investigate the effects of the Bi concentration. The most stable cluster configurations, the Bi-doping stability in the clusters, and the electronic state interaction between Bi and intrinsic defects have been studied in detail. It is found that Bi_Li⁴⁺ has a stronger electron-capturing ability than Nb_Li⁴⁺ in Bi-doped congruent LiNbO₃. The Bi_Li-doping-induced local lattice distortion and the electron-trapping behavior remain unchanged with increasing Bi-doping concentration. However, the position of the Bi defect states in the band gap is found to be shifted in congruent LiNbO₃. This is mainly attributed to the large lattice relaxation induced by the large number of Li vacancies instead of the ionic level redistribution caused by the direct interaction between Bi and intrinsic defects.