Evidence of Chlorotellurate(IV) – Hydroxochlorotellurate(IV) species equilibrium upon dissolution of tellurite glasses in aqueous hydrochloric acid: A Raman spectroscopic study

Abstract

Raman spectroscopy has been used to elucidate the structure of tellurium (IV) oxide and its binary mixtures with thallium oxide both in the glassy state and in aqueous hydrochloric acid solutions. The addition of Tl2O in pure TeO2 glass results in the progressive transformation of TeO4 trigonal bipyramid (tbp) to TeO3 trigonal pyramid (tp) units in agreement with the literature findings. Thallium oxide acting as a modifier for the tellurite network, reduces the functionality of the initial unit and lowers the continuous network rigidity. The spectral changes upon dissolution of the 0.2Tl2O-0.8TeO2 glass in aqueous hydrochloric acid solution have also been measured revealing that the main structural units of the glass structure did not survive in a solution state and the connectivity of the glass network has completely collapsed. The systematics and the concentration dependence of the spectra acquired from different solutions indicate the presence of several chlorotellurate(IV) and hydroxochlorotellurate(IV) ionic species. The spectroscopic data are interpreted in such a way in order to indicate a dynamic equilibrium between the TeCl62− anion and the TeCl4(OH)− species. A combined analysis of the polarized and depolarized scattered intensity is presented here which aimed at elucidating the presence of additional species including the TeCl4(OH)22− and TeCl3(OH) species, respectively. The proposed model is discussed in the framework of the current phenomenological status of the field.