Der Jahn-Teller-Effektdes Cu2+-Ions in tetraedrischer Sauerstoffkoordination

Abstract

The ligand field reflectance spectra of tetrahedrally coordinated Cu2+-ions in different oxidic host structures (several spinel compounds, Ca2ZnSi2O7 , Zn2SiO4 , several garnets, ZnO) and at different temperatures (300 °K - 4 °K) are analysed. For Cu2+-ions in compressed tetrahedra with D2d-symmetry the two expected bands: 2B2(2T2) → 2E (2T2) [t1] and 2A1 (2E) [t3] respectively were found, while in cases of lower symmetry the transition 2B2(2T2) → 2B1(2E) [t2] is observed in addition. For the spinel mixed crystal series [Zn1-xCux] (4) [Cr2] (6)O4 (0≦x ≦ 1,0) a first order transition from the cubic to a tetragonal (c/a < 1) structure occurs at :r = 0.47. The transitions t1 and t3 show a remarkable UV-shift for x>0,47, indicating an increasing Jahn-Teller distortion of the CuO4- tetrahedra with increasing x. The Jahn-Teller-splitting of the 2T2-groundstate [t1] was found to range between ≈ 3000 cm-1 and 8500 cm-1 for the different compounds. The bands could be fitted using "angular overlap" parameters eλ (λ = σ, π⊥, π||). Finally the spectrum of Cu2+-doped ZnO could be analysed on the basis of trigonally compressed CuO4-tetrahedra with a 2T2-groundstate splitting of ≈ 3000 cm-1.