Glass heat capacity and its abrupt change in glass transition region

Glass transition (GT) has been a fascinating, but challenging subject in the condensed matter science over decades. Despite progress in understanding GT, many crucial problems still need to be clarified. One of the problems deals with the microscopic origin of abrupt change of heat capacity (Cp) around glass transition. Here we study this problem through two approaches. First, we analyze the Cp change with temperature on homologous series of glass formers (i.e., with regular compositional substitution). Second, we do the same on non-homologous systems (e.g. without regular compositional substitution) or glass systems of different bonding types (covalent, metallic and ionic bonds). In addition, we discuss how chemical bond is associated with glass Cp (at T < Tg) for different glass types. We explain why the Cp values of most oxide glasses at Tg agrees with Dulong-Petit law, but some not. We cover a large range of glass formers from metallic to non-metallic glasses. To conduct this study we convert the units of all the Cp data from J/mol K and J/g K to J/g-atom K. This study will provide insight into the correlations among chemical bonding, microstructure structure, liquid fragility, glass Cp, and abrupt Cp change at Tg.
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