The Crystalline Structure of Ice

Abstract

Only one form of natural ice has been proved to exist at ordinary pressures. The positions of the oxygen atoms are known definitely from X-ray investigation. These form an open-work structure in which each oxygen is surrounded tetrahedrally by four others, the whole system having hexagonal symmetry. The positions of the hydrogen atoms between each pair of oxygens are not known with certainty, perhaps because they may be continually changing. Curious diffuse X-ray patterns, which are related to the temperature of ice, have yet to be explained in detail, but may throw light on the atomic movements. A cubic form of ice may exist at temperatures below −70° C. and under special conditions, and some less symmetrical high pressure forms have also been studied.