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4.1 Self‐organization and the Intermediate Phase

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Self‐organization designates chemical and/or topological rearrangements in a network that take place spontaneously to reduce the overall energy in the system [21]. An important consequence of this process is that it allows a system to exist as an isostatic network over a range of coordination numbers or compositions. This range is sometimes known as the intermediate phase or reversibility window [22]. The range depends on the system considered and, to some extent, on its thermal history as well as on the property being measured (e.g. enthalpy release during relaxation, Raman frequency shifts in glasses, or activation energy of viscosity). For example, a coordination number range from 2.39 to about 2.52 has been reported for the intermediate phase in GexSe(1−x) system from Raman frequency shifts [22], and a range from r = 2.35 to about 2.45 in the (Na2O)x(SiO2)(1−x) system from enthalpy relaxation [23]. Interestingly, Wang et al. [24] found no evidence of any intermediate phase in the Ge–As–Se system. Also, Shatnawi et al. [25] found no discontinuities or breaks but only smooth variation with respect to composition in the structural response of GexSe(1−x) glasses in the range 0.15 < x < 0.40 implying the absence of any phase transition associated with the start and end of the intermediate phase range.

Encyclopedia of Glass Science, Technology, History, and Culture

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