Formation and annealing of cubic ice: II. Kinetic study

A new structure model (Hansen et al 2008 J. Phys.: Condens. Mater. 20) of ice Ic, so-called 'cubic ice'(Konig 1943 Z. Kristallogr. 105 279), allows the description of the complex diffraction pattern in terms of stacking fault probabilities and anisotropic particle size. To understand the successive transitions when going from metastable recovered high-pressure phases via ice Ic towards the stable ice Ih, as previously observed (Kuhs et al 1989 Z. Kristallogr. 186 174, Kuhs et al 2004 Phys. Chem. Chem. Phys. 6 4917), two samples of deuterated ice Ic from ice IX and ice V have been studied in situ as a function of time at temperatures between 145 and 240 K at the neutron powder diffractometer D20 at ILL. Small changes of stacking fault probability occur hours after formation at about 165 K and continue gradually upon heating towards a higher proportion of hexagonal at the expense of cubic stacking sequences. At 190 K the intensities of the Bragg reflections change considerably and the peaks become sharper. The pattern now increasingly resembles, but does not match exactly, the one of ice Ih until a temperature of about 240 K is reached (Koza et al 2005 Phys. Chem. Chem. Phys. 7 1423). We will show quantitatively the time evolution of stacking disorder and crystallite size at different temperatures for ice Ic of different origin obtained from neutron powder diffraction. Small angle neutron scattering with D11 at ILL backs the observations.