Crystallization Kinetics of Pb20Ge17Se63 and Pb20Ge22Se58 Chalcogenide Glasses

Abstract

Two glasses of the chalcogenide system Pb₂₀Ge_xSe_80-x, with x =17 and 22 at.%, were prepared by the melt quench technique. Differential scanning calorimetry emphasized that the investigated Pb₂₀Ge₁₇Se₆₃ and Pb₂₀Ge₂₂Se₅₈ glasses are crystallized to GeSe₂ and PbSe₂ as well as GeSe₂ and PbSe, respectively as revealed by X-ray diffraction analysis. It was found that the glass transition temperatures of the Pb₂₀Ge₂₂Se₅₈ glass are higher than those of Pb₂₀Ge₁₇Se₆₃ ones. The respective values for the activation energy of glass transition (E _t ) for Pb₂₀Ge₁₇Se₆₃ and Pb₂₀Ge₂₂Se₅₈ are found to be 434±20 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 crystallization (E _c) before and after annealing were determined using different methods. Applying the modified Johnson-Mehl-Avrami (JMA) equation, it could be found that GeSe₂ is crystallized by surface crystallization, while both PbSe₂ and PbSe are crystallized by bulk crystallization in three dimensions .