Structure and correlation in liquid alloys by X-ray and neutron diffraction

Abstract
A method for obtaining information about correlation in a liquid or amorphous alloy is presented. The explicit structure in a binary could in principle be determined from three independent diffraction patterns. It is relatively much simpler to measure and analyse the x-ray and neutron intensity patterns and with these alone obtain considerable correlation information, even if more than two atom types are present, by calculating the ratio of the two experimental radial distributions. For the binary the relevance of the ratio derives from the fact that each distribution is a sum of the radial distributions of the three types of atom-pairs, each term being weighted by the appropriate product of scattering amplitudes. The structure of the sample can be analysed by comparing the ratio for any interatomic distance to the values it would have for pure A-A, pure B-B, pure A-B, and random pairing. In a true liquid the results are semiquantitative. In an alloy with well-defined short-range order, the correlation of these close pairings can be clearly determined. Results are shown for liquid NaK and vitreous silica. For any alloy the experimental results would serve to test structural models.

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