Proton ordering dynamics of H2O ice

From high precision measurements of the complex dielectric constant of especially prepared samples of H 2 O, we identify the onset temperatures of the phase transition into and out of ice XI from ice I h to occur at T I h -XI = 58.9 K and T XI-I h = 73.4 K. For D 2 O, T I h -XI = 63.7 K and T XI-I h = 78.2 K. A triple point is identified to exist at 0.07 GPa and 73.4 K for H 2 O and 0.08 GPa and 78.2 K for D 2 O where ices I h , II and XI coexist. A first order phase transition with kinetic broadening associated with proton ordering dynamics is identified at 100 K. Proton ordering in ice I h and nucleation of ice XI domains are observed for the first time in undoped H 2 O and D 2 O; the ice I h /II/XI triple point is also identified.