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Nature Physics 2, 414–418 (1 June 2006) | doi:10.1038/nphys313

Annealed high-density amorphous ice under pressure

Richard J. Nelmes , John S. Loveday , Thierry Str|[auml]|ssle , Craig L. Bull , Malcolm Guthrie , G|[eacute]|rard Hamel & Stefan Klotz

The well-known expansion of water on cooling below 277|[nbsp]|K is one of several peculiar properties that could signal a second critical point near 220|[nbsp]|K and 0.1|[nbsp]|GPa in pressure, deep in the supercooled liquid phase. Evidence for this would be a first-order transition line between two distinct supercooled liquids at temperatures below the critical point. As that lies below the minimum crystallization temperature, experimental tests have instead used low-|[nbsp]|and high-density amorphous ices—LDA and HDA—as proxies for the supercooled liquids. But numerous studies over the past decade have not yielded a clear consensus about the nature of the HDA/LDA transition. Here we identify a previously uncharacterized state of high-density amorphous ice obtained if HDA is annealed at pressures near 2|[nbsp]|kbar. The transition between this annealed HDA and LDA is strikingly different from the behaviour found in earlier work, in a way that favours the two-liquid model.