Nucleation and crystallization kinetics of rapidly quenched lithium pyrophosphate glass

• Preparation of 66.7Li2O–33.3P2O5 mol% glassy electrolyte using rapid quenching
• Nucleation rate is calculated as 3.1 × 1018 m− 3 s− 1 at 583 K for the glass.
• Li4P2O7 crystallizes as the primary phase; LiPO3 appears as a secondary phase.
• Li4P2O7 and LiPO3 both obey three-dimensional crystal growth mechanism.
• Number of nuclei increases as Li4P2O7 grows while for LiPO3 they remain constant.

66.7Li2O–33.3P2O5 mol% glass prepared by twin-roller rapid quenching has been chosen to investigate the nucleation and crystallization kinetics using differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and high temperature X-ray diffraction (XRD) as the experimental tools. Such studies assume importance in designing materials for solid state ionic devices. The glass exhibits a nucleation rate of 3.1 × 1018 m− 3 s− 1 at a typical temperature of 583 K and crystal growth rate of 2.1 × 10− 2 nm s− 1 at 643 K. Non-isothermal DSC studies reveal that the glass undergoes bulk crystallization with an activation energy of 114 kJ mol− 1. The crystallized phase is identified as lithium pyrophosphate (Li4P2O7). Crystallization kinetic studies reveal that Li4P2O7 crystallizes three dimensionally with increasing number of nuclei. Interestingly, lithium metaphosphate (LiPO3) appears as a secondary phase in the glass matrix, however, the final glass ceramic product obtained after prolonged heat treatment of the glass is single phase Li4P2O7. The secondary phase also grows three dimensionally with an activation energy of 365 kJ mol− 1, but with constant number of nuclei in contrast to Li4P2O7. The high nucleation and growth rate with lower activation energy for crystallization of Li4P2O7 underscore that the glass is extremely prone to nucleation and crystallization.