THERMAL CRYSTALLIZATION BEHAVIOR OF AS-TE GLASSES

Thermal crystallization behavior of As.Te100-x (25 less-than-or-equal-to x less-than-or-equal-to 60) glasses is studied by differential scanning calorimetry. AsxTe100-x glasses with x < 40 are found to exhibit one glass transition and one crystallization reaction, during heating. On the other hand, glasses with 40 less-than-or-equal-to x less-than-or-equal-to 50 show one glass transition and two crystallization reactions. Unlike other binary telluride glasses, the first crystallization reaction in AsxTe100-x glasses does not correspond to the precipitation of hexagonal Te. It corresponds to the formation of a metastable intermediate crystalline phase, which transforms into the equilibrium As2Te3 phase at the second crystallization reaction. As a consequence of this difference in the crystallization behavior, AsxTe100-x glasses with 40 less-than-or-equal-to x less-than-or-equal-to 50 do not show the phenomenon of double glass transition. Further, the two crystallization reactions of these glasses are found to merge progressively, with the increase in arsenic content. As a result, AsxTe100-x glasses with 50 < x less-than-or-equal-to 60 show only one crystallization reaction. An explanation for this interesting crystallization behavior of AsxTe100-x glasses is provided with the help of x-ray diffraction, electron microscopy, and thermogravimetry studies.