Different heating/cooling cycles were performed to check the stability of the composites and physical mixtures upon heating as well as Tgs after the first cycle. The maximum temperature applied in these DSC experiments was 320 °C, to avoid recrystallisation of the inorganic glass. During the first upscan of the physical mixtures, a broad endothermic peak between 30 and 140 °C is observed and related to the release of adsorbed water during the first cycle (Fig. ). The presence of a glass transition at Tg (~297 °C) confirms the glassy nature of 50(Na2O)-50(P2O5). This Tg value is maintained after three upscans for all the materials (both physical mixtures and composites), where second and third upscans are almost equivalent in all cases (Fig. ). A reduction in the Tg overshoot on the second up-scans was observed for the three MOF-CIGCs, which may again be attributed to relaxation processes above Tg (Fig. ). Structural relaxation in supercooled liquids is related with the atomic rearrangements during isothermal annealing processes. Comparing the DSC curves of the inorganic glass with the composites and physical mixtures, it is clear that the presence of ZIF-8 within the glass matrix appears to delay the recrystallization process, relative to that of the ball-milled sample. This is more evident in the case of the composites than physical mixtures (i.e. prior to pelletisation and thermal treatment) (Fig. ).