Crystallization kinetics of Pb20Ge17Se63 and Pb20Ge22Se58 chalcogenide glasses

Two glasses of the chalcogenide system Pb20GexSe80-x, with x=17 and 22 at.% , were prepared by the melt quench technique. Differential scanning calorim etry emphasized that the investigated Pb20Ge17Se63 and Pb20Ge22Se58 glasses are crystallized to GeSe2 and PbSe2 as well as GeSe2 and PbSe, respectivel y as revealed by X-ray diffraction analysis. It was found that the glass tr ansition temperatures of the Pb20Ge22Se58 glass are higher than those of Pb 20Ge17Se63 ones. The respective values for the activation energy of glass t ransition (E-t) for Pb20Ge17Se63 and Pb20Ge22Se58 are found to be 434 +/- 2 0 and 761 +/- 77 kJ mol(1), while those for the annealed samples are 928 +/ - 85 and 508 +/- 23 kJ mol(1), respectively. The activation energies of cry stallization (E-c) before and after annealing were determined using differe nt methods. Applying the modified Johnson-Mehl-Avrami (JMA) equation, it co uld be found that GeSe2 is crystallized by surface crystallization, while b oth PbSe2 and PbSe are crystallized by bulk crystallization in three dimens ions.