X-ray and neutron diffraction studies on amorphous transitionmetal - boron alloys (Fe-B, Co-B, Ni-B)

The atomic-scale structure of the amorphous metallic alloys Fe80B20, Co81sub(.)5B18sub(.)5, and Ni81sub(.)5B18sub(.)5 was investigated by X-ray- and neutron-diffraction covering a wide range of the ratio (f metal/f boron) of the scattering factors of both components. The structure factors S(q) show a pronounced dependence on the ration f metal/f boron. 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 f metal/f boron also partial coordination numbers could be obtained. The results suggest some kind of short range order between the metal and the boron atoms. (orig.)