Influence of thermal and thermoelectric treatments on structure and electric properties of B2O3-Li2O-M2O5 glasses


A transparent glass with the composition 60B(2)O(3)-30Li(2)O-10Nb(2)O(5) (mol%) was prepared by the melt quenching technique. The glass was heat-treated with and without the application of an external electric field. The as-prepared sample was heat-treated (HT) at 450, 500 and 550 degrees C and thermoelectric treated (TET) at 500 degrees C. The following electric fields were used: 50 kV/m and 100 kV/m. Differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman, dc and ac conductivity, as a function of temperature, were used to investigate the glass and glass-ceramics properties. LiNbO3 crystals were detected, by XRD, in the 500 degrees C HT, 550 degrees C HT and 500 degrees C TET samples. The presence of an external electric field, during the heat-treatment process, improves the formation of LiNbO3 nanocrystals at lower temperatures. However, in the 550 degrees C HT and in the TET samples, Li2B4O7 was also detected. The value of the sigma(dc) decreases with the rise of the applied field, during the heat-treatment. This behavior can indicate an increase in the fraction of the LiNbO3 crystallites present in these glass samples. The dc and ac conduction processes show dependence on the number of the ions inserted in the glass as network modifiers. The Raman analysis suggests that the niobium ions are, probably, inserted in the glass matrix as network formers. These results reflect the decisive effect of temperature and electric field applied during the thermoelectric treatment in the structure and electric properties of glass-ceramics. (C) 2007 Elsevier B.V. All rights reserved.




Materials Science


Graca, MPF; Da Silva, MGF; Valente, MA

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