Characterization and thermoanalytical investigations of silver tellurite

Abstract

Silver tellurite, prepared by precipitation, crystallized in tetragonal form and DSC studies show that it undergoes phase transformations on heat-treatment in the temperatuae ranges 578-604 K and 695-717 K. X-ray diffractometry suggests that in the first transformation, which is irreversible, the tellurite transforms to monoclinic form. The second transformation is reversible and the high temperature phase reverts back to the monoclinic form on cooling. The reversible phase transformation could be ascertained by electrical resistivity and reflectance spectrum measurements. The kinetic parameters, computed from the DSC data, show that the energy of activation, entropy of activation and the frequency factor are high. This is attributed to the effectiveness of a large number of vibrations. Numerous tellurites have been described in the literature and these have been studied to understand their structure and other related properties [1][2][3][4][5]. Investigations on silver tellurite, prepared by precipitation, show that it undergoes phase transformations on heat-treatment [3]. However, there appear to be no papers on the characterisation of the phases formed and on the mechanism of these transformations. In the present investigation, silver tellurite, prepared by precipitation, has been subjected to thermogravimetric and differential scanning calorimetric analysis to ascertain thermal effects. Different phases have been identified by X-ray diffractometry and chemical analysis. Magnetic susceptibility and electrical resistivity, as functions of temperature, and room temperature reflectance spectra have been recorded to gain further information. From the thermal data, kinetic parameters have been computed.