The glass transition in high-density amorphous ice.

Area of Science:

• Materials Science
• Physical Chemistry
• Condensed Matter Physics

Background:

• The glass transition in low-density amorphous ice (LDA) has been a long-standing controversy, particularly regarding its behavior above 136 K.
• High-density amorphous ice (HDA) is metastable at ambient pressure but becomes less so at higher pressures, making its glass transition a key area of study.

Purpose of the Study:

• To review and clarify the glass transition behavior of high-density amorphous ice (HDA).
• To differentiate the glass transition temperatures of LDA, HDA, and very high-density amorphous ice (VHDA).

Main Methods:

• Review of experimental findings on amorphous ice transitions.
• Analysis of pressure-temperature (p-T) phase diagrams and glass transition temperatures (Tg).

Main Results:

• Experimental observations suggest distinct glass transition temperatures for LDA and HDA.
• The glass transition of HDA was observed at 116 K at ambient pressure, differing from LDA's transition.
• Evidence suggests that previous studies at higher pressures may have probed the glass transition of very high-density amorphous ice (VHDA).

Conclusions:

• Low-density amorphous ice (LDA) and high-density amorphous ice (HDA) exhibit clearly separated glass transition temperatures.
• Three distinct glass transition lines can be defined in the p-T plane for LDA, HDA, and VHDA, resolving prior ambiguities.