Profile analysis of amorphous haloes by means of a Fourier transformation, with special reference to the structures of amorphous Pt-C and Ni-P

A Fourier transform method is proposed for the analysis of halo profiles from amorphous materials, which is analogous to the Fourier method for the analysis of Debye-Scherrer line profiles as originally expounded by Warren & Averbach [J. Appl. Phys. (1950), 21, 595]. Applied to the first haloes of amorphous alloys, it gives radial distribution functions in which only those atom pairs are represented whose separations are atomic diameters or integral multiples thereof. The method is applied to the first haloes of amorphous Pt-C and Ni-P, which correspond to the nearest neighbour distances of metallic atoms. The result from amorphous Pt₂₀C₈₀ confirms the microcrystalline model with diameter 2 × 2.27 Å. The analysis of amorphous Ni₈₃P₁₇ gives a result less simple to understand. The correlation between neighbouring atoms extends as far as 5 × 2.2 Å, which explains the sharpness of the first halo observed. Directly neighbouring pair separations are found to be increased by 0.2~0.4 Å. The definition of amorphous scattering is discussed in relation to that in very broad Debye-Scherrer reflections.