Structural transitions in amorphous H2O and D2O: the effect of temperature

We have recently observed amorphous-amorphous transitions incurred upon decompressing very high density amorphous ice (VHDA) at 140 K from 1.1 to <0.02 GPa in a piston-cylinder setup by monitoring the piston displacement as a function of pressure and by taking powder x-ray diffractograms of quench-recovered samples (Winkel et al 2008 J. Chem. Phys. 128 044510). Here we study the effect of changing the temperature from 77 to 160 K during decompression from 1.1 to <0.02 GPa, and the effect of substituting D2O for H2O at 140 and 143 K. At 77 K all structural transitions are arrested and six-coordinated VHDA is quench recovered. At 125-136 K the continuous transition to five-coordinated expanded high density amorphous ice (eHDA) takes place. At 139-140 K, both the continuous transition to eHDA and the quasi-discontinuous transition to four-coordinated LDA are observed, i.e. VHDA -> eHDA -> LDA -> At 142-144 K, crystallization to mixtures of cubic ice Ic and ice IX is observed prior to the quasi-discontinuous transition, i.e. VHDA -> eHDA -> ice Ic/ice IX. At 160 K ice Ic is recovered, which most likely transforms from a high-pressure ice (HPI) such as ice V, i.e. VHDA -> HPI -> ice Ic. Exchanging D2O for H2O at 140 K does not significantly affect the amorphous-amorphous transitions: both the decompression curves and the powder x-ray diffractograms are unaffected within the experimental resolution. However, at 143 K D2O-VHDA can be decompressed according to the sequence VHDA -> eHDA -> LDA, i.e. crystallization can be suppressed at similar to 3 K higher temperatures.