X-ray and neutron diffraction studies of the structure of dilute solutions of Au in Pb. II. Neutron measurements of bulk equilibrium lattice parameters

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Abstract
For pt.I see ibid., vol.14, p.1073 (1984). A double-crystal backscattering neutron spectrometer has been used to perform a careful measurement of the difference in lattice parameter between pure Pb and Pb+640 at.PPM Au. The results in the single-phase region at temperatures above 200 degrees C show that the Pb(Au) lattice contracts with respect to pure lead with increasing temperature. This contraction is explained by the conversion of Au2 dimers to single substitutional defects. A quantitative analysis shows that the substitutional gold atom contracts the lattice by about -1 AA per Au atom, while the Au2 dimer expands the lattice only slightly by 0.3 AA per dimer. At 215 degrees C the concentration of substitutional gold is 380-500 PPM and the concentration of dimers is 70-130 PPM.