Journal of Non-crystalline Solids | 2019
Theoretical investigations on the EPR parameters and local structures for V4+ in alkali niobium borate glasses
Abstract
Abstract EPR parameters and local structures for V4+ in xNb2O5•(30-x)A2O•69B2O3 (NAB, where A\u202f=\u202fLi, Na, K; x\u202f=\u202f0, 4, 8\u202fmol%) glasses are theoretically studied using the perturbation formulas of EPR parameters for tetragonally compressed octahedral 3d1 clusters. From the quasi-linear concentration variations for covalency factor N, tetragonal compression ratio ρ and core polarization constant κ with only three adjustable coefficients, the concentration dependences of EPR parameters are suitably interpreted. N increases linearly for NLB (0.839–0.864) and NNB (0.801–0.811) with x (0–8\u202fmol%) but shows the quadratic decrease for NKB (0.802, 0.807, 0.801 at 0, 4 and 8\u202fmol%), whereas ρ and κ decrease linearly. For different alkali metal A at the same x, N decreases with increasing ionicity of A, while ρ and κ increase due to declining force constant of V4+–O2– bond and enhancing vanadium 3d-3\u202fs (4\u202fs) orbital admixtures, respectively.