The electron paramagnetic resonance (EPR) spectra of VO2+ ions in the 15 NaI-(15 - x)Na2O-xK(2)O-B2O3 mixed alkali glass system mere analysed at X-band frequencies at 310 K. The spin-Hamiltonian parameters and covalency rates were evaluated. It was found that the V4+ ions exist as vanadyl (VO2+) ions and are in an octahedral coordination with a tetragonal compression. The covalency rates (1 - alpha(2)) and (1 - upsilon(2)) indicate moderate covalency for the sigma- and the pi-bonds. It was observed that the spin-Hamiltonian parameters depend slightly on the relative alkali ion concentrations of K and Na. (C) 1999 Elsevier Science B.V. All rights reserved.

Glasses in the ternary and quaternary systems viz. xNaI-(30- x)Na2O-70B(2)O(3) and 1SNaI-(15-x)Na2O-xLi(2)O-70B(2)O(3) were prepared by melt quenching method. Different experimental techniques like XRD, conductivity, Optical absorption and ESR were used to characterize these glasses. The conductivity of the glasses xNaI- (30-x)Nn(2)O-70B(2)O(3) was found to vary in a non-linear manner with the composition 'x'. The highest conductivity glass composition 15NaI-15Na(2)O-70B(2)O(3) was used as an electrolyte in the fabrication of a solid state cell and its discharge characteristics were investigated. An electrochemical decomposition potential of 2.89 V was deter-mined for the cell, Various cell parameters were evaluated. The effect of mixed alkali ion on the spectral characteristics was investigated in the glass system 15NaI-(15-x)Na2O-xLi(2)O-70B(2)O(3) with the help of ESR and Optical data. The Delta g(1) values were found to vary in a non-linear manner with the composition exhibiting a maximum for x=9, indicating that the inter-action energy between the two cations reaches a maximum at x=9. The observed changes may be attributed to the mixed alkali effect.