Characteristics of La2CaB10O19 crystallization from glass

The characteristics of La2CaB10O19 (LCB) crystallization from a La2O3–CaO–B2O3 glass were studied. The crystal growth rate (U) was estimated from the crystalline layer thicknesses to obtain the activation energy for growth (EG), which was found to be 418 kJ/mol. The activation energy for overall crystallization (E), obtained from non-isothermal differential thermal analysis (DTA) by the methods of Kissinger and Ozawa, was in the range of 398–417 kJ/mol. A comparison of the activation energies showed that E ≅ EG. X-ray diffraction (XRD) patterns, light microscopy images and second harmonic generation tests, confirmed that LCB is the dominant phase crystallizing from the glass. Nucleation-rate type curves derived from DTA measurements showed that the annealed glass behaved as a nuclei site-saturated matrix. Transmission electron microscopy and selected area electron diffraction images of fine glass powders indicated the presence of crystalline clusters of 30–50 nm, which are related to the phases detected by XRD. The crystallization of LCB from the glass was characterized by a growth process from a nuclei site-saturated matrix and could be analyzed by the Johnson-Mehl-Avarmi kinetic model.