Deuteron ordering in ice containing impurities: A neutron diffraction study

We measured neutron powder diffraction of 0.13-M KOD-doped D2O ice at temperatures in the range of 52-80 K to investigate the growth mechanism of ice XI, a deuteron-ordered phase of ice Ih. We observed that the diffraction profiles of the doped ice change with time in the temperature range of 67-74 K. To obtain the mass fraction f (the ratio of mass of ice XI to that of the doped ice), we carried out Rietveld analysis using a two-phase model. The results show that the growth rate of ice XI increases and approaches the transition temperature T c=76 K. The f value reaches 0.125 in about 3 days of measurement at a temperature just below T c. Further, we found that the growth rate is accelerated by annealing the ice at temperatures lower than 64 K for sufficient time in advance to produce ice XI. We conclude that the temperature history of an ice sample is important for understanding the growth mechanisms of ice XI