Melt Homogenization and Self‐Organization in Chalcogenides‐Part II

Abstract

The compositional variation of the non‐reversing enthalpy at Tg, ΔHnr(x), in GexSe100−x glasses decreases abruptly by an order of magnitude as x increases to xc(1) = 19.5(5)%, the rigidity transition, and then remains minuscule till x increases to xc(2) = 26.0(5)%, when the term abruptly increases by an order of magnitude as glasses become stressed‐rigid. The rigid but unstressed networks formed in between these two transitions represent the Intermediate Phase (IP). The square‐well like variation of ΔHnr(x), also known as the reversibility window develops sloping walls, then a triangular shape and eventually disappears as glasses of increasing heterogeneity are studied. The ΔHnr term ages over weeks outside the IP but not inside the IP. Raman line shapes of as‐quenched melts are quite similar to those of Tg‐cycled glasses for compositions in the IP, but not outside the IP– an optical analog of the thermal reversibility window. Variations of Molar volumes, display a global minimum in the IP and a pronounced increase outside that phase. Physical behavior of dry and homogeneous chalcogenide glasses that leads to sharp elastic and chemical phase transitions remains to be understood theoretically. The physics of network may be even more interesting than hitherto recognized.