Part 1: X-Ray High-Angle Scattering and Ultrasonic-Measurements

Abstract

Abstract By means of X-ray scattering and ultrasonic experiments, the structure of different melts of the Cd-Ga system was investigated. The structure factors S (q) obtained for the pure elements agree well with those reported by other authors. The concentration dependence of the structure factors shows no special features. From the structure factors, the total pair-distribution functions were calculated by a Fourier transformation. The nearest-neighbour distances, obtained from the total pair-distribution functions, amount to 3.04 Å for pure Cd and 2.83 Å for pure Ga and are nearly constant for all alloys. The concentration dependence of the experimental nearest-neigh-bour distances and coordination numbers was determined and is compared with statistical distribution and macroscopic segregation models. These comparisons tend to indicate a preference for like-atom neighbours. From the long-wavelength limit S(0) of the structure factors of Cd and Ga, the isothermal compressibilities were calculated. These show a satisfactory agreement with those calculated from adiabatic sound velocity data. The anomalous ultrasonic absorption of a single melt with nearly critical concentration indicates the existence of concentration fluctuations. This result is in agreement with those obtained by X-ray smallangle scattering experiments which are described in Part 2 of this work [1].