Temperature dependence of the pressure-induced amorphization of ice Ih studied by high-pressure neutron diffraction to 30 K
Résumé
High-pressure neutron diffraction allowed the in situ observation of the pressure-induced amorphization of ordinary ice Ih between 130 and 30 K, i.e., to lower temperatures than any other diffraction study before. We find that the pressure required for complete transformation into high-density amorphous ice !HDA" increases with decreasing temperature to #80 K but remains approximately constant below. Our findings support earlier evidence of two distinct mechanisms responsible for the pressure-induced amorphization in ice Ih, namely, amorphization due to mechanical melting down to lowest temperatures, and amorphization due to thermal melting at elevated temperatures. Such scenario naturally explains why HDA prepared through compression at 77 K is structurally distinct from the form of HDA obtained by the compression of low-density amorphous ice !LDA" and hence cannot be associated with the hypothesized high-density proxy of liquid water in a two-state model.