Formation and growth of ice XI: A powder neutron diffraction study

Abstract: We measured neutron diffraction profiles of powdered KOD-doped D2O ice to investigate the formation and growth of ice XI, a deuterium-ordered phase of ice, from ice Ih, a disordered phase. During the measurements, the ice was annealed at 57K for about 17h, and then warmed up and kept at 68K for about 55h, which are below the transition temperature . The diffraction profiles for the doped ice at 57K did not change with time and were close to those for ice Ih with the deuterium-disordered arrangement. However, when the temperature increased from 57 to 68K, the diffraction profiles changed. We carried out the Rietveld analysis with the parameters for a two-phase model to obtain the structural evidence of the appearance and the growth of ice XI. The analysis provided evidence of ice XI as space group Cmc21 at 68K. The temporal increase of the mass fraction of ice XI showed that nucleation of ice XI began just after warming up to 68K. Then, ice XI grew for several days in the doped ice. This study provides first structural observations of the growth of ice XI. [Copyright &y& Elsevier]