Valence and coordination of chromium ions in ZnO-Sb 2O 3-B 2O 3 glass system by means of spectroscopic and dielectric relaxation studies

Abstract

ZnO-Sb 2O 3-B 2O 3 glasses containing different concentrations of chromium ions (introduced as CrO 42-) 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 σ ac 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 Cr 6+ state, occupy network forming positions with CrO 42 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 Cr 6+ state to Cr 5+ and Cr 3+ states. A gradual transformation of chromium ions from tetrahedral positions to octahedral positions could also be established from these results. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.