Relaxation Behaviour of Lithium-Borosilicate Glasses

Three systems of lithium borosilicate (LBS) glasses namely SI 42.5Li2O: (57.5-x) B2O3: xSiO2, SII 42.5Li2O: xB2O3 :( 57.5-x) SiO2 where x=0, 5, 10, 20, and 30, and SIII (100-2x) Li2O: xB2O3: xSiO2 where x=30, 28.75, 27.5, 25, and 22.5, are prepared using conventional melt quenching technique. Functional dependence of conductivity on temperature in the range from 523- 673K and frequency in the range from 10Hz to 13 MHz is studied. In order to analyze electrical conductivity the microscopic parameters such as ionic jump distance and barrier height are necessary. These parameters can be understood properly on the basis of the models proposed by Almond and Elliott. As frequency increases from 1MHz to 13MHz, the Tmin shifts towards low temperature side. According to this model the charge transfer is a thermally activated process and provides a correlation between the barrier height (W) and the hopping length (R). The fitting of conductivity data into Almond-West type power law behavior σ = σ(o) + Aωs yielded power law exponent(s). Electrical conductivity data fitted well in Elliott’s model, which is true only for amorphous materials. The temperature dependence of frequency exponent s exhibits a minimum (smin) at a particular temperature (Tmin) . . From the scaling behavior of the ac conductivity it is seen that all the curves scaled better, suggesting that s is temperature independent. It is observed that smin shifts to lower temperature, which shows that electrical conductivity of glassy solid electrolytes is the manifestation of ionic dynamic processes. The superposition of the reduced conductivity at all temperatures shows relaxation mechanism is temperature independent. Analysis of modulus formalism with a distribution of relaxation times using KWW stretched exponential function, the stretching exponent, β, is depend on temperature. The analysis of the temperature variation of the M″ peak indicates the relaxation process is thermally activated.