The structure of liquids as revealed by the analysis of their radial distribution functions

Published data on radial distribution functions of liquid argon and of many cubic face-centred and body-centred liquid metals at different temperatures (as well as of solid copper at two different temperatures) have been analysed by the method proposed earlier [Bagchi (1970). Advanc. Phys. 19, 119]. Analysis of the results shows that the liquid state consists of clusters of distorted microcrystallites whose linear dimensions vary from 50 to 150 Å. Relative lattice distortion near the melting point is around 10% for f.c.c. structures and 8% for b.c.c. structures. It is shown that from the standpoint of diffraction theory such a structure of the liquid state is equivalent to the two-phase model underlying the significant structure theory of liquids proposed by Eyring and coworkers. Thus the liquid state represents an assembly of small thermodynamic systems. It is suggested that the first order phase transition is caused chiefly by the breakdown of a statistically homogeneous assembly of atoms representing crystals and gases into a statistically inhomogeneous system.