钙钛矿型晶体的倍频系数和离子位移、能带结构间的关系

RELATIONSHIP BETWEEN SHG COEFFICIENTS AND METAL IONIC DISPLACEMENT,ENERGY BAND STRUCTURE FOR PEROVSKITE AND TUNGSTEN-BRONZE TYPE CRYSTALS

1974年作者提出了“非线性光学效应的离子基团理论”[1]:,并据此对钙钛矿型等体系的倍频系数作了理论计算,得到了很好的结果。本文进一步使用作者1981年建议的“晶体倍频系数的平均能带近似计算法”[2],从能带理论出发计算了钙钛矿型晶体的倍频系数。计算结果表明:(1)由“平均能带近似法”仍可得到“钙钛矿型晶体倍频效应基团理论”[1]的几个基本论点,并给出后者的近似等级;(2)充分揭示了 SrTiO_3、KTaO_3晶体电场感应倍频系数X_(333)^(2ω)/X_(311)^(2ω)比值的变化与中心B离子的相对位移、能带结构、B-O键离子性之间的关系;(3)通过倍频系数和能带结构关系的研究,有可能把晶体倍频系数作为检验能带结构是否正确的一个新的数据;(4)由本文的计算公式,可以计算出在外电场作用下中心B离子相对于配位体氧原子的位移量△Z,并和外电场作用下的感应自发极化P_5的实验值相一致。

In this paper we will discuss SHG coefficients for perovskite -type NLO crystals from the viewpoint of energy band theory. The anionic group theory - localized molecular orbital model for NLO effect in crystals -is equivalent to an average energy band approximation method,which can not only obtain the basic structure - property relationship between the micro-structure and NLO effect in the NLO crystals given by anionic group theory but also elucidate what kind of approximations there are in the model. Inaddition, the approximation method can yet describe the relationship between the change of the ratio X(2ω)333/X(2ω)311 and the displacement ΔZ of the central metal ion relative to its oxygen ligand, energy band structure, as well as ionicity of metal-oxygen bond.