Sub-T_g enthalpy relaxation in an extremely unstable oxide glass and its implication for structural heterogeneity

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• 作者：Yanfei Zhang ; Lina Hu ; Shujiang Liu ; Chaofeng Zhu ; Yuanzheng Yue
• 关键词：Sub-Tg annealing ; Enthalpy relaxation ; Structural ordering ; Structural heterogeneity ; Crystallization
• 刊名：Journal of Non-Crystalline Solids
• 出版年：1 December, 2013
• 年：2013
• 卷：381
• 期：Complete
• 页码：23-28
• 全文大小：989 K

文摘

We study the sub-T_g relaxation in an extremely unstable glass former, i.e., 65SiO₂-35Al₂O₃, and its relation to structural heterogeneity (e.g., structurally ordered domains in glass matrix). This is done by hyperquenching (~ 10⁶ K/s) the liquid, then annealing the hyperquenched (HQ) glass below T_g and subsequently scanning the annealed HQ glass in a differential scanning calorimeter (DSC). The results show that structural ordering can take place even below T_g. An endothermic pre-peak is observed when the HQ sample is annealed at 0.75T_g for sufficiently long time, which is, however, much weaker compared to that of stable glass formers subjected to same annealing conditions. We also investigate the effect of the sub-T_g annealing on crystallization above T_g. The results imply that some structurally ordered domains exist already in the liquid state. The ordered domains lower the activation energy for further structural ordering during the sub-T_g annealing, and thereby lowers the activation energy for crystal growth above T_g.