In situ Raman and optical microscopy of the relaxation behavior of amorphous ices under pressure

The transformation of low-density amorphous (LDA) ice produced from high-density amorphous (HDA) ice was studied up to 400 MPa as a function of temperature by in situ Raman spectroscopy and optical microscopy. Changes in these amorphous states of H2O were directly tracked without using emulsions to just above the crystallization temperature T-x. The spectra show significant changes occurring above similar to 125 K. The results are compared with data reported for the relaxation behavior of HDA, to form what we call relaxed HDA, or rHDA. We find a close connection with expanded HDA (eHDA), which is reported to exist as another metastable form in this P-T region. The observation of this temperature-induced LDA transition under pressure complements the previously observed pressure-induced reversible transition between LDA and HDA at 120-140 K. Copyright (C) 2009 John Wiley & Sons, Ltd.