In the past fifteen years, several studies have been performed towards obtaining joint neutron and X-ray analysis of samples under extreme conditions, at high pressure in particular (McMahon et al., 2013 Guthrie, 2015 ). The precision of the structural parameters was improved by a factor of up to 50% in the XN refinement compared with refinements using the X-ray or neutron data separately.Ĭoupling X-ray and neutron diffraction techniques provides the highest-quality structural information about a molecular solid in crystalline form (Finney, 1995 Schmidtmann et al., 2014 ). The two data-sets were combined in a single `XN' structure refinement in which all atoms, including H atoms, were refined with anisotropic displacement parameters. The highly penetrating diffracted neutron beams passing through the metal body of the miniature cell as well as through the diamonds yielded data suitable for structure refinement, and compensated for the low completeness of the X-ray measurements, which was only 24% on account of the triclinic symmetry of the sample and the shading of reciprocal space by the cell. The sample, of dimensions 0.40 × 0.22 × 0.20 mm 3 and held at a pressure of 0.71 GPa, was contained in a miniature Merrill–Bassett diamond-anvil cell.
In this study, diffraction data have been collected under the same conditions on the same sample of copper(II) sulfate pentahydrate, using a conventional laboratory diffractometer and source for the X-ray measurements and the Koala single-crystal Laue diffractometer at the ANSTO facility for the neutron measurements. This is a disadvantage when the sample is studied at high pressure because it is very difficult to achieve exactly the same pressure in two separate experiments, especially if the neutron data are collected using Laue methods where precise absolute values of the unit-cell dimensions cannot be measured to check how close the pressures are. Single-crystal X-ray and neutron diffraction data are usually collected using separate samples.
0 kommentar(er)
