Introduction

Vast masses of ice and snow on the Earth play an important part in our life. Nevertheless, ice is not a traditional topic in solid state physics. This is explained by difficulties of making controlled and reproducible experiments with ice for the following reasons.

First, ice has a large number of solid modifications: hexagonal or ordinary ice, Ih; cubic ice, Ic; ices II–IX; vitreous ice. Most of them exist at elevated pressure or need special formation conditions. Under ordinary conditions, only hexagonal ice is formed, which has therefore been investigated more frequently than other modifications. In this chapter we shall deal only with ordinary ice.

Second, ice is an unusual example of the solid state, since it consists of two very different parts: a crystalline, hard lattice of oxygen atoms and a disordered, quasi-liquid proton system. For this reason, the physical properties of ice are intermediate between those of a solid and a liquid.

Third, as a rule ice contains various impurities, whose distribution, homogeneity and concentration are very hard to control and which strongly affect the physical properties of ice.

In spite of such difficulties, by the beginning of the 1970s the essential principles of ice physics had been formulated. Using them it is possible to explain the unusual properties of ice and to predict the behaviour of ice under different conditions.