Determination of chemical order of manganese–germanium liquid alloy by the ‘null matrix method’

Abstract The Bhatia–Thornton concentration–concentration partial structure factor, SCC(q), is a strong indicator of the order in liquid alloys. Manganese is one of the four metals, which has a negative neutron scattering length, while the one for germanium is positive. Thus for a defined composition (Mn69Ge31) the linear combination of the two neutron scattering lengths weighted by the atomic compositions is zero (zero alloy). We present here the results of neutron diffraction studies on the Mn69Ge31 at 980 °C ‘null matrix alloy’. The measured total structure factor is proportional to the Bhatia–Thornton SCC(q) (‘null matrix method’). The main peak of the experimental SCC(q) is a proof of a strong chemical order in this alloy. This order also appears in real space determined by the Fourier transform of the structure factor. From the experimental Bhatia–Thornton concentration–concentration partial structure factor SCC(q), we have extracted the ordering potential in the alloy, which is the difference of the effective potential between atoms of the same species and the effective potential of atoms of different species. The ordering potential indicates clearly that the alloy is heterocoordinated. Simple effective potential models like the hard sphere one, cannot be used to interpret the structure.