KCdF3晶体中Cr3+-Li+中心局域结构研究

利用零场分裂参量与晶体结构之间的定量关系,研究了双掺杂晶体KCdF₃:Cr³⁺,Li⁺的局域结构。指出,对于KCdF₃:Cr³⁺,Li⁺晶体,四角晶场的形成包含两个方面:(1)由于电荷补偿而产生的等效电荷形成的四角对称晶场;(2)Cr³⁺的局域结构发生晶格畸变而产生的四角对称晶场。事实上,当Cr³⁺和Li⁺掺入KCdF₃晶体时,Cr³⁺代替了Cd²⁺离子;由于Cr³⁺离子与Cd²⁺离子的半径不同、电荷不同、质量不同,导致Cr³⁺的局域结构发生晶格畸变,由此而产生四角对称晶场;由于电荷补偿,Li⁺离子取代了[001]方向与Cr³⁺离子邻近的Cd²⁺离子,由此产生的等效电荷而形成的四角晶场。这样,Cr³⁺的局域结构由O_h对称变为C_4v点对称。文中建立了ZFS参量和晶体结构之间的定量关系。在考虑晶格畸变和等效电荷的基础上,研究了KCdF₃:Cr³⁺,Li⁺晶体的ZFS参量,理论结果和实验符合很好。得到了F^-离子向中心离子分别移动为ΔR₁=0.00268nm,ΔR₂=0.001nm,ΔR₃=0.00165nm。

Local Structure Study of Cr3+-Li+Centres in KCdF3 Crystals

The aim of the work is to study the local struture of KCdF₃ doped with Cr³⁺ and Li⁺ ions by means of the quantitative relationship between the ZFS parameter and the crystal structure.The present work suggests that the tetragonal crystal field of Cr³⁺ ion in KCdF₃:Cr³⁺,Li⁺ crystals comes from following two origins:(1) The equivalent charge caused by the charge compensation in the [001]-axis direction. (2) The lattice distortions of the nearest-neighbor fluorine coordination.In fact,when Cr³⁺ and Li⁺ ions doped into KCdF₃ crystals, Cr³⁺ ions replace divalent Cd²⁺ ions. Owing to the difference in charge, mass, and radius between Cr³⁺ and Cd²⁺ ion, the lattice distortion occurs to the local structure of Cr³⁺-Li⁺ centres in KCdF₃ crystals. Due to the charge compensation, a Cd²⁺ ion on [001]-axis will be replace by Li⁺ ion. Because of these, the local structure distorts and local point symmetry around Cr³⁺ changes from O_h to C_4v. According to the idea,the relationship between the zero field splitting D and crystal structure for Cr³⁺ in KCdF₃:Cr³⁺,Li⁺ crystals has been established by means of the superposition model and third order perturbation theory.The EPR zero field splitting parameter D has been investigated,taking account of both effect of lattice distortion and the equivalent charge.The calculated result(D=-0.06203cm^-1) is in excellent agreement with experimental result(D=-0.06212(5)cm^-1).Meanwhile,the results,the F^- ion moves toward the central Cr³⁺ ion by ΔR₁=0.00268nm,ΔR₂₁=0.001nm,ΔR₃=0.00165nm,are obtained.