20LiF-xSb(2)O(3)-(79.6-x)B2O3:0.4CuO glasses with the value of x (ranging from 9.6 to 49.6 mol% in steps of 10%) were prepared. Dielectric properties (constant epsilon', loss tan delta, ac conductivity, sigma(ac), over a range of frequency and temperature and breakdown strength) of these glasses have been studied. The results of these studies were analyzed with the aid of data on optical absorption, and ESR spectra on these glasses. The analysis suggests that there is a gradual, transformation of Cu2+ ions from covalent environment to ionic environment in the glass network with an increase in the,concentration of Sb2O3. (c) 2004 Elsevier B.V. All rights reserved..