Dielectric relaxation and glass transition dynamics in melt-quenched ZIF-62 glass

Metal-organic framework (MOF) glasses have recently emerged as a distinct class of coordination materials with properties inaccessible in their crystalline counterparts, yet their glassy-state dynamics remain largely unexplored. Here, we report a comprehensive dielectric spectroscopic study of a ZIF-62-based MOF glass, complemented by structural and thermal characterizations with X-ray Diffraction (XRD), Infrared Spectroscopy (FTIR), scanning electron microscopy (SEM), and Differential Scanning Calorimetry (DSC). A complex relaxation landscape in the vicinity of the glass transition temperature (Tg) is revealed, consisting of multiple secondary relaxation processes and a structural relaxation. The pronounced non-Arrhenius behavior of the structural relaxation indicates a significantly cooperative nature of the movement of the metal-ligand coordination network and suggests a fragile nature of the ZIF-62 glass in terms of a large dielectric fragility (m=113.6±15.3). The abnormal dynamic features of the secondary relaxations upon vitrification suggest that these localized motions are considerably coupled with the rearrangement movement of the coordination network. These results demonstrate that MOF glasses exhibit hierarchical and dynamically coupled relaxation behavior distinct from conventional inorganic and polymeric glass formers.