Investigations of the local distortions and EPR parameters for Cu in xNa O-(30-x)K O-70B O (5 ≤ x ≤ 25 mol%) glasses.

The local distortions and electron paramagnetic resonance parameters for Cu in the mixed alkali borate glasses xNa O-(30-x)K O-70B O (5 ≤ x ≤ 25 mol%) are theoretically studied with distinct modifier Na O compositions x. Owing to the Jahn-Teller effect, the octahedral [CuO ] clusters show significant tetragonal elongation ratios p ~19% along the C axis. With the increase of composition x, the cubic field parameter Dq and the orbital reduction factor k exhibit linearly and quasi-linearly decreasing tendencies, respectively, whereas the relative tetragonal elongation ratio p has quasi-linearly increasing rule with some fluctuations, leading to the minima of g factors at x = 10 mol%. The composition dependences of the optical spectra and the electron paramagnetic resonance parameters are suitably reproduced by the linear or quasi-linear relationships of the relevant quantities (i.e., Dq, k, and p) with x. The above composition dependences are analyzed from mixed alkali effect, which brings forward the modifications of the local crystal-fields and the electronic cloud distribution around Cu with the variation of the composition of Na O.