Structure solution of oxides from zone axes precession electron diffraction data

We present several examples of crystal structures solved by precession electron diffraction which cover a great domain of different structures from very small to very large unit cells, having very high or low symmetry, containing light or heavy elements or both. A common point of these samples is that they were synthesized as powders. X-ray powder diffraction encountered difficulties in solving these structures because the powders were a mixture of phases or because the peak overlap was too severe due to large unit cell parameters. The influence of various experimental parameters and data exploitation procedures on the successful structure solution are investigated. It is shown in particular that the amount of data available is the most influential parameter, whereas the precision of the intensity measurement or of the determination of the structure factor amplitudes from the intensities is of less importance provided that the experimentally strong reflections correspond to the high structure factor amplitudes. This is precisely the achievement of the precession electron diffraction method, which reduces multiple scattering, while in standard selected area electron diffraction multiple scattering leads to intensities that do not show a clear correlation between intensities and structure factor amplitudes.