DEVITRIFICATION BEHAVIOR OF GLASSES IN THE LEAD TETRAGERMANATE-LITHIUM TETRAGERMANATE COMPOSITION RANGE

The effect of replacing PbO by Li2O on the glass structure, on the gla ss transition temperature and on devitrification behaviour in a series of glasses in the lead tetragermanare-lithium tetragermanate composit ion range has been studied by differential thermal analysis, X-ray dif fraction and Fourier-transform infrared spectra. The anion network of all glasses contains GeO4 and GeO6 groups in the same molar ratio. The glass transition temperature is increased by the progressive replacem ent of Pb2+ by Li+ ions. All glasses, except the lead tetragermanate g lass, exhibit internal crystal nucleation without any addition of nucl eating agent. The crystallizing phases have been identified and relate d to devitrification mechanisms.