Isothermal crystallization and effect of soak time on phase evolution, microstructure and ionic conductivity of Li2O-Al2O3-TiO2-P2O5 glass-ceramic

Glass-ceramics derived from Li2O-Al2O3-TiO2-P2O5 vitreous system were obtained by isothermal heat treatment at 700 degrees C, for different soak times ranging from 0 to 60 h. Phase analysis revealed mixture of amorphous and crystalline phases for short soak times (<1 h). By 1 h of soak time, crystallization was complete and phases were ascribed to dominant Li1+xAlxTi2-x(PO4)(3) (LATP) along with secondary AlPO4 and TiO2, previously reported. Microstructural evolution with soak time was imaged using high resolution scanning electron microscope (SEM). Crystalline volume fraction in glass-ceramics was estimated from image analysis and it followed Kolmogorov-Johnson-Mehl-Avrami (KNA) equation. Conductivity of glass-ceramics was derived using impedance spectroscopy data for all soak times and correlated to the crystalline volume content After attaining a critical volume of crystalline phase/s, conductivity increased significantly and was observed to follow the scaling equation sigma(dc) similar to (V - V-c)(beta), where sigma(dc) is dc conductivity, V is crystalline volume content, V-c is threshold value of crystalline volume content above which sudden increase in conductivity was observed and beta is scaling exponent V-c approximate to 30% was in accordance with percolation scaling law and is attributed to formation of 3D conducting channel network in the glass-ceramics microstructure. (C) 2016 Elsevier B.V. All rights reserved.