Formation of Ba2NaNb5O15 Crystal and Crystallization Kinetics in BaO-Na2O-Nb2O5-SiO2-B2O3 Glass

We have synthesized Ba2NaNb5O15 (BNN) crystal by annealing 25.6BaO-6.4Na(2)O-32Nb(2)O(5)-24SiO(2)-12B(2)O(3) (BNNSB) glass and investigated the crystallization kinetics from the glass. The glass sample was prepared by a plate quenching method. Thermal, structural, vibrational, and surface properties have been studied by using differential thermal analysis, X-ray diffraction, Raman spectroscopy, and atomic force microscopy, respectively. It is found that the crystallite sizes of the orthorhombic Ba2NaNb5O15 crystal occurring in the BNNSB glass are confined within 30-70 nm. The Williamson-Hall plot was applied to estimate the effect of crystallite size and strain to Bragg peak broadening. The isothermal model of the Johnson Mehl Avrami Kolmogorov function was applied to characterize the kinetics of the crystallization process. The Avrami exponent 4.5 indicates that the crystallization mechanism belongs to an increasing nucleation rate with diffusion-controlled growth. The activation energy of crystallization, 5.0 eV, obtained from the isothermal model, shows a value similar to that resulting from the isoconversion method. The Raman scattering patterns, which are very different between the crystalline and glass phases, have been deconvoluted, and the various vibrational modes have been explained based on the network dimensionality, nonbridging oxygen, and the degree of structural order.