The mean size of the ordered domains is about 5 nm. This implies that the formed crystals in TVP glass, which are induced by hydration under different RH conditions, have a nano-size. These nanocrystals lead to the Bragg peaks in the XRD patterns (Fig. ). To explore the origin of the exothermic peaks at 718 K and 683 K in DSC upscans (the black lines in Fig. ) of both 65RH and 85RH samples, respectively, as well as to verify the stability of the crystals, i.e., H4V3P3O16.5•xH2O, formed during the hydration process, these two samples were heattreated at 718 and 683 K for 6 hours, respectively. The XRD patterns of 65RH, 85RH and the heattreated samples are shown in Fig. . Strikingly, the Bragg peaks which are assigned to H4V3P3O16.5⋅