Investigations on the g Factors for the Tetragonal and Orthorhombic Cu2+ Centers in YBa2Cu3O7–δ

Abstract

The local structures and the g factors of two Cu2+ centers in YBa2Cu3O7–δ are theoretically studied by using the perturbation formulas of the g factors for a tetragonal and an orthorhombically elongated octahedral 3d9 clusters. The crystal-field parameters in these formulas are determined from the superposition model and the local distortions due to the Jahn–Teller effect. Based on the calculations, for the tetragonal Cu2+ center in YBa3Cu2O7, the Cu-O bonds are found to suffer the axial elongation of about 0.032 A along the c-axis due to the Jahn–Teller effect. For the orthorhombic Cu2+ center in Y2BaCuO5, the Cu-O bonds is found to experience the axial elongation δZ (≈ 0.078 A) along the c-axis and the planar bond length variation δX (≈ 0.012 Ǻ) in the perpendicular (ab) plane, responsible for the axial anisotropy Δg (= gz − (gx + gy)/2 = 0.168) and the perpendicular anisotropy δg (= gx – gy = 0.081). The theoretical g factors are in good agreement with the experimental data. The local structures of both Cu2+ centers are discussed.