Structure of liquid KTl investigated by means of neutron diffraction using 205Ti isotope substitution and reverse Monte Carlo modeling

In recent neutron diffraction measurements on liquid KT1 a prepeak was observed in the structure factor at a rather low value of the wavevector: k = 8 nm(-1) [1] This indicates a periodicity in real space of 0.93 nm, which was assumed to be due to Tl-clustering. Additional neutron diffraction experiments using Tl-205 isotope substitution confirm unambiguously that the Tl-Tl correlation is responsible for the intermediate-range order in liquid KTl. Over the last few years we have acquired structure data on liquid KTl using several instruments. We use this collection of data in order to investigate the usefulness of the Reverse Monte Carlo technique for modeling liquid alloys. First, we examine how the different statistical accuracies of the experimental data effect the results obtained by RMC modeling. Second we compare the RMC models obtained with and without isotopic substitution. We conclude that the different statistical accuracies of our measurements without isotope substitution lead to similar RMC results. Accuracy of the isotopic data, however, is important since the difference in the total scattering by KTl and (KTl)-Tl-205 is only 12%. The RMC model that was eventually obtained using the isotopic data differs significantly from the models for single data sets. This indicates that one single measurement of the structure factor of liquid KTl is insufficient for the determination of the structure, even when RMC is being used.