Theoretical Studies on the Local Structures and EPR‐ g Factors for the Orthorhombic Cu ²⁺ Centers in GdBa ₂ Cu ₃ O 7‐Δ and La 0.5 Gd 0.5 Ba ₂ Cu ₃ O y

The local structures and the electron paramagnetic resonance (EPR) g factors of Cu 2+ centers in GdBa 2 Cu 3 O 7‐Δ and La 0.5 Gd 0.5 Ba 2 Cu 3 O y are theoretically studied by using the perturbation formulas of the g factors for an orthorhombically elongated octahedral 3d 9 cluster. In these formulas, the crystal‐field parameters (CFPs) are determined from the superposition model and the local distortions due to the Jahn–Teller (JT) effect. Based on the calculations, the Cu‐O bond lengths are found to experience the axial elongations δ z (≈0.052 and 0.055 Å) along the c ‐axis and the planar bond length variations δ r (≈0.061 and 0.128 Å) in the perpendicular ( ab ) plane for the orthorhombic Cu 2+ centers in GdBa 2 Cu 3 O 7‐Δ and La 0.5 Gd 0.5 Ba 2 Cu 3 O y , respectively. The calculated g factors are in good agreement with the experimental data. The local structures of both Cu 2+ centers are discussed.