Mobile Bjerrum defects: A criterion for ice-like crystal growth

There has recently been a substantial increase in information on low-temperature phase transformations of ice and ice-like substances along with a rapid increse in molecular level information on the defect structure and activity of this subset of hydrogen-bonded solids. These data, some quantitative and some qualitative in nature, are examined from the viewpoint that the phase transformation mechanism depends on the availability of mobile orientational defects (Bjerrum L defects) within the new phase. Some of the data that seem particularly apt for establishing any dependence of the phase transformation on the presence of mobile L defects within the new phase, reflect a strong correlation between transformation rates/temperature and the availability of mobile L defects. One possible inference is that the integrity of a growing phase can be maintained only if defects responsible for orientational mobility at the interface can ultimately achieve equilibrium through recombination. The implications of such a dependence on mobile L defects are examined for a variety of systems. For example, one implication is that, at low temperature (<160 K), the structure I clathrate hydrate of trimethylene oxide (TMO) should grow more rapidly than the structure II hydrate, since structure I hydrates are known to be relatively rich in mobile defects. New data for the clathrate hydrates of TMO are presented that confirm the preferential growth of the structure I hydrate from amorphous deposits containing water and TMO in ratios ranging from 7:1 to >17:1.