X-ray and neutron scattering

Abstract:

The structures of chemically identical amorphous zeolitic amorphous frameworks (ZIFs), which were prepared from crystalline ZIF-4 via three different routes, are compared by refining atomistic models against their neutron and X-ray total scattering data. The diffraction data are very similar at all but the lowest values of momentum transfer and this is reflected in the ability of models with the same continuous random network topology to fit the data from each of the three amorphous ZIFs. Despite this there are differences in the detail; the relative positions of the lowest-Q peak in the Zn-Zn partial structure factors are consistent with differences in the densities of the different amorphous samples, and peaks in the ZIF-4 glass total scattering structure factors are in general broader, suggesting shorter-ranged correlations.

Abstract:

Using a combination of single-crystal neutron scattering and reverse Monte Carlo refinements, we study the magnetic structure of paramagnetic MnO at a temperature (160 K) substantially below the Curie-Weiss temperature |θ|∼550 K. The microscopic picture we develop reveals a locally ordered domain structure that persists over distances many times larger than the correlation length implied by direct analysis of the spin-correlation function. Moreover, the directional dependence of paramagnetic spin correlations in paramagnetic MnO differs in some important respects from that of its incipient ordered antiferromagnetic state. Our results demonstrate that atomistic refinement to large three-dimensional neutron-scattering datasets is a practical approach, and have implications for the understanding of paramagnetic states in weakly frustrated systems, including high-temperature superconductors.