Structure of molten bi-cu alloys by means of cold neutron scattering in the region of small momentum transfer

Abstract

Abstract In the present work scattering experiments with cold neutrons are described, which were done with molten Bi-Cu alloys in the region of small momentum transfer (0.08 Å−1 < k < 1.5 Å−1). Using the time-of-flight method of analysis for the scattered neutrons, the inelastically scatterered neutrons were separated from the elastically scattered neutrons. The coherent scattering cross section was obtained by integration as the area below the quasielastic line and shows a strong increasing tendency with smaller momentum transfer, especially for the molten alloys in the mid-concentration region. This can be explained by the existence of regions with one kind of atoms within the molten alloys. These inhomogeneities are considered from a more dynamic point of view according to Ornstein and Zernike as concentration fluctuations, the correlation length of which can be determined to be approximately 2Å. Using the more static interpretation according to Guinier, the regions can be regarded as so-called clusters with spherical shape. These clusters consist either of Cu or of Bi atoms and have a diameter of about 6Å, which corresponds to the diameter of the first coordination shell. With a melt containing 50 at.% Bi, the scattering cross section in the direction of the primary beam decreases by about 40% when the temperature is increased from 800 to 1100°C, the diameter of inhomogeneities remaining nearly constant.