| Glass structure, rigidity transitions and the intermediate phase in the Ge -As -Se ternary (2000) | |||||||||||||||
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| Abstract. – The non-reversing heat flow, ∆Hnr(x) nearTg in ternary GexAsxSe1−2x glasses is examined by temperature-modulated differential scanning calorimetry. The ∆Hnr(x) term shows a deep minimum (which is almost zero) in the 0.09 <x<0.14 range, identified with the intermediate phase, and an increase, both at low x (< 0.09) in the floppy phase and at high x (> 0.14) in the stressed rigid phase. Expressed in terms of mean coordination number, ¯r =2+3x, the large width, ∆¯r = rc(1) − rc(2) = 0.15, of the intermediate phase and its low onset value rc(1) = 2.27 are shown to be consistent with the presence of Se = As(Se1/2)3 units in addition to pyramidal As(Se1/2)3 and tetrahedral Ge(Se1/2)4 units in the stress-free backbone. The vanishing of ∆Hnr(x) intheintermediate phase is in harmony with the notion that the number of Lagrangian constraints/atom exhausts the three available degrees of freedom, and leaves the backbone in a mechanically stress-free state. Introduction. – A floppy-to-rigid transition in network glasses was predicted [1, 2] in the early 1980’s. The transition has enjoyed widespread interest in science, not only because the glass forming tendency is optimized near this transition, but also because it serves as a paradigm of percolative transitions in condensed matter [3], and computational complexity | |||||||||||||||
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