The distribution of Cr atoms in Fe${}_{100-x}$Cr${}_x$ alloys with $x⩽25$ within the first two coordination shells, 1NN–2NN, around probe ${}^{57}\mathrm{Fe}$ atoms was studied using Mössbauer spectroscopy. Clear evidence was found that the distribution is not random but instead characteristic of a given atomic configuration $(m,n)$ ($m$ being the number of Cr atoms in 1NN and $n$ in 2NN). The behavior was described quantitatively in terms of average short-range order (SRO) parameters $\langle {\alpha }_1\rangle$ (for 1NN), $\langle {\alpha }_2\rangle$ (for 2NN), and $\langle {\alpha }_{12}\rangle$ (for 1NN–2NN), as well as in terms of a local SRO parameter $\alpha (m,n)$ for each pair $(m,n)$. A change of sign (inversion) was found both in $\langle {\alpha }_1\rangle$ and in $\langle {\alpha }_2\rangle$, though going with $x$ in opposite directions. No inversion was observed in $\langle {\alpha }_{12}\rangle$, which was either positive or negative depending on the metallurgical state of the samples. These findings prompt a revision of current interpretation of experimental and theoretical results relevant to the issue.

• Received 26 October 2010

DOI:https://doi.org/10.1103/PhysRevB.83.180202