By X-ray diffraction and neutron diffraction using the isotopic substitution method, the partial structure factors /S

Mit dem Ziel, Hinweise auf den Grad der Ähnlichkeit zwischen dem geschmolzenen und dem amorphen Zustand zu gewinnen.

The atomic-scale structure of the amorphous metallic alloys Fe80B20, Co81·5B18·5, and Ni81·5B18·5 was investigated by X-ray- and neutron-diffraction covering a wide range of the ratio (fmetal/fboron) of the scattering factors of both components. The structure factors S (q) show a pronounced dependence on the ratio fmetal/fboron . In the cases of a small ratio an additional peak near q = 21.5 nm-1 appears in the structure factors from which a definite distance between B-B atoms, which are separated by metal atoms, is deduced. The corresponding structure factors show only weak oscillations in the range of the second and third maxima, which are followed by increased amplitudes at larger q's. By Fourier-transformation radial distribution curves were evaluated, from which the distances between the metal-metal-, the metal-boron-, and the boron-boron-atoms and the coordination numbers are extracted. From the splitted first maximum of the radial distribution function in the cases of small ratio fmetal/fboron also partial coordination numbers could be obtained. The results suggest some kind of short range order between the metal and the boron atoms.

X-ray small-angle scattering experiments were performed on nine melts of the Cd-Ga system at different temperatures up to 440°C. Evaluation of the data follows the Ornstein-Zernike theory of critical scattering, thus yielding correlation lengths £ of concentration fluctuations and the long-wavelength limit Sec (0) of the Bhatia-Thornton structure factor. Studies of the concentration and temperature dependence of £ and Sec (0) indicate that the critical point occurs at cc = 50.0 ± 1-0 at % Ga and Tc -295.2 ± 0-1° C. For a melt with the critical concentration, Sec (0) increases up to 3500 times the ideal $cc (0)=CACB-This indicates a strong segregation tendency. In the vicinity of the critical point of the Cd-Ga system, experimental correlation lengths | > 100 A were obtained. The critical-point exponents v and y were determined. It follows that the behaviour of a critical Cd-Ga melt satisfies the prediction of the classical mean-field theory for higher temperatures, whereas, within experimental accuracy, the lattice-gas predictions are satisfied upon approaching the critical temperature.

The scattering of cold neutrons (λ = 1 nm) with amorphous Fe80 11B20 yields a strong contribution at small q=4π (0.7 (nm)-1 ≤ q ≤ 2.4 (nm)-1 arising from two kinds of defects of different size : i) local defects with an extent of about 1.5 nm ii) Extended defects with an extent of about 40 to 60 nm, which are interpreted as quasi-dislocations in the amorphous material