Crystallization kinetics and phase transformation in superionic lithium metaphosphate (Li2O-P2O5) glass system

The ionic conductivity of mol% 50Li(2)O-50P(2)O(5) melt quenched glass shows an anomalous increase after its glass transition temperature (T-g) around 590 K. On further increasing the temperature gradually, the conductivity decreases owing to the devitrification of Li2O-P2O5 glass. The evolution of devitrified crystallites was evidenced by XRD patterns. To understand the devitrification process, isothermal and non-isothermal DSC studies have been carried out on mol% 50Li(2)O-50P(2)O(5) glass. T-g as well as T-c values are found to increase monotonically with increasing heating rates. Variation of T-g as a function of heating rates has been investigated to evaluate the lower limiting temperature of T-g and the activation energy for structural relaxation. Results of the DSC studies indicate (i) single-stage bulk crystallization of the glass, with DSC traces exhibiting a single amorphous double right arrow crystalline (T-c) transition, (ii) an order parameter (Avrami constant) of 2.8 +/- 0.1, suggesting internal (bulk) crystallization of the glass, (iii) an activation energy for crystallization equal to 121.7 kJ mol (1) and (iv) the activation energy for structural relaxation, E-g, to be 558.8 kJ mol(-1). The crystallization mechanism is closely associated with the JMA model and the experimental dataset have been fitted to a non-isothermal Avrami expression and the obtained parameters confirm the experimental results.