Theoretical investigations on the defect structures and g factors for W5+ in lead bismuth arsenate glasses

Electron paramagnetic resonance (EPR) g factors and defect structures for W ⁵⁺ in alkali niobium borate glasses (40– x)PbO-15Bi ₂O ₃-45As ₂O ₃- xWO ₃ (PBA, x = 1–6 mol%) are theoretically investigated from the g formulas for tetragonally compressed octahedral 5d ¹ clusters. The d-d transition bands (including the minimal at 4 mol%) for varying concentrations are satisfactorily reproduced from the Fourier type function of x. The concentration dependences of g factors are reasonably explained from the parabolic functions for covalency factor N (<<1) and relative tetragonal compression ratio ρ (~ 4%), with largely parabolically decreasing and increasing tendencies, respectively. The distinct extrema (i.e., the maxima of g factors and the minimum of cubic field parameter Dq) and the relevant quantities (i.e., the maxima of ρ and the minimum of N) at 4 mol% are illustrated as the most intense local structural modifications and electronic cloud redistributions around W ⁵⁺ arising most probably from original doped W ⁶⁺.