Investigations on the local structures and the spin Hamiltonian parameters for Cu²⁺ in (90-x)TeO₂-10GeO₂-xWO₃ glasses

The local structures and the spin Hamiltonian parameters (SHPs) for Cu²⁺ in (90-x)TeO₂-10GeO₂-xWO₃ glasses are theoretically investigated at various WO₃ concentrations (x=7.5, 15, 22.5 and 30 mol%). Subject to the Jahn-Teller effect, the [CuO₆]^10- groups are found to experience the small or moderate tetragonal elongation distortions (characterised by the relative tetragonal elongation ratios ρ ∼ 0.35-3.09%) in C₄ axis. With only three adjusted coefficients a, b and ω, the relevant model parameters (Dq, k and ρ) are described by the Fourier type and linear functions, respectively, and the measured concentration dependences of the d-d transition bands and SHPs are reproduced. The maximum of g _parallel and the minimum of vertical stroke A _parallel vertical stroke at x=15 mol% are illustrated from the abrupt decrease of the copper-oxygen electron cloud admixtures or covalency and the obvious decline of the copper 3d-3s (4s) orbital admixtures due to the decreasing electron cloud density around oxygen ligands spontaneously bonding with Cu²⁺ and Te⁴⁺ (W⁶⁺), respectively.