Many materials, ranging from minerals or catalysts to framework compounds and pharmaceuticals are not suitable for growing large crystals prohibiting single crystal X-ray analysis. Yet, introduction of nano crystallinity and special crystallographic features like disorder, defects, pseudo symmetry or stress/strain effects creates new or allows optimizing existing physical properties. With increasing complexity, special structural features and decreasing size of crystalline domains, X-ray powder diffraction becomes more and more difficult for structural characterization, which is fundamental for understanding material properties. High-resolution transmission electron microscopy (HR-(S)TEM), visualizing structural features directly at the atomic scale, introduces often beam damage whereas electron diffraction is less destructive. For a complete structure solution, delivering atomic positions in sub Ångstrom accuracy, needs three-dimensional experimental data with high completeness. Data collection from oriented nano crystals limits the amount of measurable reflections significant and thus, delivers mostly heavy atom positions but hardly lighter atoms. Dynamical scattering effects, strongly enhanced in oriented zones, reduces using electron beam precession.
Automated electron diffraction tomography [1] uses diffraction patterns from non-oriented nano crystals taken during a fixed tilt sequence. In such a way electron diffraction data collection of most of the independent reflections is possible with significantly reduced dynamical effects. Additionally, in order to integrate reflections fully the electron beam is precessed. The resulting diffraction patterns are processed with ADT3D/eADT, which, after some geometrical corrections, reconstructs the three-dimensional reciprocal space. From the 3D volume, cell parameters can be determined using clustering-routines. Subsequently, reflections indexing and intensities integration is performed. The three-dimensional reciprocal space reconstruction provides the chance to inspect the volume by eye and detect crystallographic specialties such as disorder, twinning or additional individuals.
For ADT data sets standard kinematic approach (intensities proportional to Fhkl2) delivers ab-initio the complete structural model solved by direct methods or simulated annealing. Based on ADT and ADT/PED data the solution of a wide range of crystal structures from nano particles down to 30nm was possible [2]. Large cell porous minerals, zeolites (doped and calcinated), highly beam-sensitive metal-organic frameworks, organic-inorganic hybrids, small organic molecules as well as quasicrystal approximants [3] have been successfully solved. Recent structure solutions cover high-pressure samples like the novel boron oxynitride (BON) including a direct refinement of the twinned structure [4].
References:
[1] Kolb, U., Gorelik, T., Kübel, C., Otten, M.T., Hubert, D., Ultramicroscopy, 107 (2007), p. 507
Kolb, U., Gorelik, T., Otten, M.T., Ultramicroscopy, 108 (2008), p. 763
[2] Mugnaioli E., Andrusenko I., Schüler T., Loges N., Dinnebier R., Panthöfer M., Tremel W., Kolb U., Angewandte Chem.Int. Ed., 51(28) (2012), p. 7041
[3] S. Samuha, E. Mugnaioli, B. Grushko, U. Kolb, L. Meshi, Acta Cryst. B 70(6) (2014), p. 999
[4] S. Bhat, L. Wiehl, L. Molina-Luna, E. Mugnaioli, S. Lauterbach, N. Nishiyama, U. Kolb, S. Sicolo, K. Albe and R. Riedel, Chem. Mater. 27 (2015), p. 5907
