空位缺陷对ZnNb2O6光电特性影响的第一性原理研究

铌酸盐类物质, 如LiNbO₃, KNbO₃, LnNbO₄ (Ln=Pr, La, Ga, Y)等, 表现出优良的光敏特性, 受到广泛关注, 但过渡金属类铌酸盐研究较少, 其光电特性与空位缺陷的关系尚无深入探讨。基于密度泛函理论第一性原理方法, 本研究探讨了空位缺陷对ZnNb₂O₆体系光电特性的影响。通过对各体系几何结构、电子结构和光电谱的计算与分析, 清晰展示了体系中原子电负性与几何位置对结构与电子能级的影响, 八面体中心位置原子(如Zn, Nb)对能带的贡献类似, 形成空位缺陷时, 价带位置相对固定。但电负性大的Nb原子形成空位缺陷体系时, 产生的晶格畸变程度大, 导带负移明显, 吸收边红移, 有利于光电特性的提升; 八面体顶点位置原子O形成空位缺陷时, 晶格畸变程度较小, 导带与价带均发生负移, 费米面处出现杂质能级, 造成载流子“俘获阱”, 同时对电荷的再分配产生较大影响, 导致体系光谱整体蓝移, 光电谱强度全面提升。

First Principles Study of Electronic Structure and Optical Properties of ZnNb2O6with Vacancy Defects

Niobate materials,such as LiNbO₃,KNbO₃,LnNbO₄(Ln=Pr,La,Ga,Y),etc.have attracted wide attention due to their excellent photosensitivity.However,the transition metal niobate is rarely studied,and the relationship between its photoelectric properties and vacancy defects has not been thoroughly explored.Here,the effect of vacancy defect on electro-optical characteristics of ZnNb2O₆system was studied based on first-principles of density function theory.Its geometric structure,electronic structure,and optical spectrum clearly revealed the effect of electronegativity and geometric position of atoms on the structure and electronic energy level.At the center of the octahedron,atoms,such as Zn and Nb,contributed similarly to the energy band,and had relatively fixed positions on the valance band when they formed vacancy defects.However,Nb atoms with larger electro-negativity generated larger lattice distortions,more obvious negative shifts of the conduction band,and red shifts of the absorption edge upon the formation of vacancy defects,which are conducive to improving electro-optical characteristics.Atom O at the vertices of the octahedron generated smaller lattice distortions when vacancy defects formed.However,negative shifts occurred at the conduction and valance bands,and impurity energy levels emerged on the Fermi surface,which induced the formation of"capture traps"on the charge carriers.This in turn exerted a larger influence on the redistribution of charge,resulting in a blue shift of the system in whole,and an all-round enhancement of optical spectrum intensity.