“Ab-initio ” Structure Solution of Nano-Crystalline Minerals and Synthetic Materials by Automated Electron Tomography

Many mineralogical phases, as well as new developed synthetic compounds, occur only in form of nano-crystalline materials. The structure characterization of these phases results often impossible with conventional X-ray techniques, as X-ray single crystal diffraction is not possible for crystals smaller than 10 µm and powder X-ray is limited to one-dimensional information, resulting inadequate in presence of low symmetry structures, super-structured phases and multiphase systems. Conversely, an electron beam can be focused on a spot of few nanometres, allowing single nano-crystal analysis. Well known problems related with electron diffraction are the strong dynamical effects due multiple scattering, the reduced number of reflections achievable with conventional techniques and the amorphization produced by the electron beam damage, quite fast especially for high polymerized and hydrated phases. To overcome all these problems, a new technique for automated collection of nano electron diffraction data from non-oriented zones was developed: automated diffraction tomography (ADT, [1, 2]). This technique was recently coupled with precession electron diffraction (PED, [3]), allowing the structure solution of even very complex inorganic and hybrid organic-inorganic phases