Valence and coordination of chromium ions in ZnO-Sb2O3-B2O3 glass system by means of spectroscopic and dielectric relaxation studies

ZnO-Sb2O3-B2O3 glasses containing different concentrations of chromium ions (introduced as CrO2-4) ranging from 0 to 1.0 mol% were prepared. A number of studies viz., differential thermal analysis, infrared, optical absorption, Raman and ESR spectra and dielectric properties (constant ε ', loss tan δ, a.c. conductivity σac over a wide range of frequency and temperature) of these glasses have been carried out. The results have been analyzed in the light of different oxidation states of chromium ions. The analysis indicates that when the concentration of chromium ions is ∝0.2 mol%, these ions mostly exist in Cr6+ state, occupy network forming positions with CrO2-4 structural units and increase the rigidity of the glass network. When the concentration of the chromium ions is increased beyond 0.2 mol%, these ions seem to be reduced from Cr6+ state to Cr5+ and Cr3+ states. A gradual transformation of chromium ions from tetrahedral positions to octahedral positions could also be established from these results. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)