Caracterização estrutural e cinética de cristalização do sistema vítreo TeO2–Na2O–TiO2.

Abstract

In the present study, samples were prepared in the TeO2-Na2O-TiO2 vitreous system using the melting quenching technique. The characterization was carried out using Xray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, UV-Vis, Differential Scanning Calorimetry (DSC) and optical absorption. Through these techniques it was possible to observe that changes in the thermal and structural properties occur with the incorporation of TiO2 in the glass matrix. The XRD results revealed the presence of three crystalline phases: 𝛼–TeO2, TiTe3O8 and Na2Te2O5. The FTIR indicates a strengthening of the structure with an increase in TiO2. This is due to a change in the Te–O–Te inter-chains that break down to form Te–O–Ti, however, if there is a saturation of TiO2, polyhedra of TiO4 are formed in the structure. Raman analyzes showed an increase in intensity in the bands at 460, 620 and 665 cm−1 which is related to the increase in polarizability of TeO4, structures, which become less distorted. With the formation of these units of TeO4, there may be a discontinuity of the Te-–𝑒𝑞O𝑎𝑥–Te bonds, which is related to the addition ofNa2O in the system, due to a material change. The exchange of Na2O por TiO2 increases the density values (𝜌), which is directly linked to changes in structure, this may be due to the difference in molar mass of the compounds.The molar volume values (V𝑚) show an opposite behavior of 𝜌. The values of oxygen packing density (OPD) indicate an increase in the packaging in the structure of the glass network with an increase of TiO2. The Band Gap energy (E𝑔) indicates that this system has an allowed indirect transition band. These results indicate that E𝑔 tends to decrease with the addition of TiO2 concentration. The Urbach tail has the lowest values for the sample 80-15-05, indicating a low disorder in the system. The ion polarizability showed an inverse behavior of the expected, this is related to the increase of simple Te–O– Ti bonds. The thermal parameters, such as the glass transition (T𝑔),crystallization onset temperature (T𝑥) and temperature on the crystallization peak (T𝑝), and the crystallization process were studied using DSC measurements. These parameters indicate a shift to higher temperatures with the addition of TiO2. The activation energy and the Avrami exponent were obtained for each peak of the Gaussians. The results were determined by the Kissinger and Vázquez models that point to nucleation with crystalline growth, with different growth conditions.