Mauro Gemmi | PubMed Health

PubMed2006

Structure solution with three-dimensional sets of precessed electron diffraction intensities.

The use of the precession technique for obtaining three-dimensional (3D) sets of electron diffraction intensities suitable for structure solution is discussed. The minerals uvarovite and åkermanite have been used as testing structures. The electron diffraction data sets obtained on these samples retain an acceptable linear relation with calculated structure factor amplitudes. The quality of these data is suitable to solve both structures using direct methods opening the possibility to use 3D precession ED data for solving unknown mineral structures.

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PubMed2003

Structure of Ti2P solved by three-dimensional electron diffraction data collected with the precession technique and high-resolution electron microscopy.

The crystal structure of Ti(2)P has been analysed using electron diffraction and high-resolution electron-microscopy techniques. A new unit cell was found, the compound is hexagonal with a = 19.969 (1) and c = 3.4589 (1) A. The structure was first solved in space group P-62m in projection using direct methods on electron diffraction data from the [001] zone axis. A three-dimensional solution was obtained using again direct methods but on a three-dimensional set of electron diffraction data recorded with the precession technique. Ti(2)P is a distorted Fe(2)P structure and, based on high-resolution images, it is possible to explain that the tripling of the unit cell is due to the ordering of P vacancies that reduces the symmetry to P-6.

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