Structure determination of a new phase Ni8Ti5 by electron diffraction tomography.

The structure of Ni 8 Ti 5 was solved and refined from precession electron diffraction tomography data using dynamical refinement approach. It has trigonal symmetry R -3 m ( a = 12.24(5) Å, c = 15.33(5) Å) with a structure related to the structure of Ni 4 Ti 3 . The greatest challenge of the structure determination was the assignment of atomic types due to the proximity of scattering powers of Ti and Ni. Several approaches to determination of atom type distribution over atomic positions were used; (1) analysis of the Wyckoff position multiplicities, (2) refinement of displacement parameters, and (3) geometrical analysis of the structure and comparison with known structures. These approaches consistently pointed to one distribution, which was confirmed by a significant improvement of the refinement figures of merit. [ABSTRACT FROM AUTHOR]