An Investigation of Local Structures and Spin Hamiltonian Parameters for Cu²⁺ in xBaO–(30–x)TeO₂–10TiO₂–58B₂O₃ Glasses

The local structures and the spin Hamiltonian parameters (SHPs) for Cu²⁺ in xBaO–(30–x)TeO₂–10TiO₂–58B₂O₃ (BTTB) glasses are theoretically investigated for various BaO concentrations (x = 10, 15, 20, and 25 mol %) in a uniform way. Attributed to the Jahn–Teller effect, the [CuO₆]^10– groups are found to experience the moderate tetragonal elongation distortions (characterized by the moderate relative tetragonal elongation ratios ρ ≈ 5.1–7.8%) along the C₄ axis. With only three adjusted coefficients a, b, and ω, the relevant model parameters (Dq, k, ρ, κ, and H) are suitably described by the quasi-second order harmonic functions, and the measured concentration dependences of the d–d transition bands and SHPs are soundly reproduced. All the model parameters show fluctuations with the concentration x, reflecting the non-monotonic variations of the local crystal-field strength, electron cloud distribution and relative tetragonal elongation distortion with x.