Characterization of lithium borate-bismuth tungstate glasses and glass-ceramics by impedance spectroscopy

Transparent glasses in the system (1-x)Li2B4O7-xBi(2)WO(6) (0 less than or equal to x less than or equal to 0.35) were prepared via melt quenching tec hnique. Differential thermal analysis was employed to characterize the as-q uenched glasses. Glass-ceramics with high optical transparency were obtaine d by controlled heat-treatment of the glasses at 720 K for 6 h. The amorpho us nature of the as-quenched glass and crystallinity of glass-ceramics were confirmed by X-ray powder diffraction studies. High resolution transmissio n electron microscopy (HRTEM) shows the presence of nearly spherical nanocr ystallites of Bi2WO6 in Li2B4O7 glass matrix. Capacitance and dielectric lo ss measurements were carried out as a function of temperature (300-870 K) i n the frequency range 100 Hz-40 MHz. Impedance spectroscopy employed to rat ionalize the electrical behavior of glasses and glass-ceramics suggest the coexistence of electronic and ionic conduction in these materials. The ther mal activation energies for the electronic conduction and ionic conduction were also estimated based on the Arrhenius plots. (C) 3001 Published by Els evier Science B.V.