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

The crystal structure of Ti2P 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) Angstrom. The structure was first solved in space group P (6) over bar 2m 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. Ti2P is a distorted Fe2P 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) over bar.