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. Thef 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. (c) 2006 Elsevier B.V. All rights reserved.