Pair Correlations in Liquid and Solid Aluminum

Abstract

Radial density functions were determined by x-ray diffraction for solid aluminum at 25, 325, and 655°C and for liquid aluminum at 665 and 750°C. Computer techniques were used to minimize the effects of experimental errors, of uncertainties in the scattering factors, and of termination errors. It was assumed that the thermal atomic displacements in solid aluminum follow a Gaussian distribution, and the resultant Debye temperatures were 383, 362, and 322°K for specimens at 25, 325, and 655°C. The first ten coupling factors, averaged for the three temperatures, were 0.70, 0.73, 0.92, 0.90, 0.82, 0.83, 1.00, 0.96, 0.93, 0.93. The radial density functions of liquid aluminum at 665 and 750°C were quite similar. Liquid aluminum has the same basic structure as liquid lead, but a different structure from that of liquid mercury. Comparisons with the random packing model showed that this model does not reproduce the details of the measured radial density function. A quasicrystalline model, in which the radial density function of the solid is broadened and damped by the introduction of a cell size and liquid diffusive motions, agreed quite well with the experimental density function. A tunnel model, in which atoms move freely in tunnels arranged in a two-dimensional close-packed network, also fitted quite well, but a large number of free parameters is required.