FTIR Investigations of the crystallization of IR-transmitting glasses: application to calcium gallate glass

Abstract

Crystallization of 60CaO·39Ga₂O₃·Fe₂O₃ glass has been studied by FTIR transmission spectroscopy. A continuous decrease in the IR transmittance (T) is observed after critical isothermal annealing, owing to the formation of CaGa₂O₄ and CaFe₂O₄. The JMA (Johnson–Mehl–Avrami) plot, In[–In(1–x)]vs. In t, gives a linear relationship when the crystallized fraction (x) can be approximated by the decreased fraction of T. The slope of the straight line in the JMA plot is ca. 1.0, which indicates two-dimensional crystallization occurring at the surface layer. The activation energy (E_a) obtained from the Arrhenius plot, 3.3 ± 0.4 eV, is identical to the Ga–O bond energy (2.9 eV) obtained from the literature. These results suggest that the cleavage of the Ga–O bond triggers the crystallization at the surface. The FTIR method is compared to the Kissinger plot in the DTA study, from which we obtain the overall E_a in the bulk.