Structure solution of the new titanate Li4Ti8Ni3O21 using precession electron diffraction

A sample having stoichiometry Li[Ti1.5Ni0.5]O4 has been synthesized to obtain a spinel structure. The resulting crystalline powder revealed a multiphase nature with spinel as the minor phase. The main phase is a new trigonal phase having a=5.05910(1), c=32.5371(1) A. The structure has been solved by direct methods working on a three-dimensional set of intensities obtained from a precession electron-diffraction experiment, and refined on synchrotron powder diffraction data in the space group P anti 3c1. The model consists of hexagonal layers of edge-sharing octahedra occupied either by the heavy cations Ti and Ni, or preferentially by Li. On the basis of cation-site occupancies the stoichiometry becomes Li4Ti8Ni3O21, which is compatible with the microanalysis results. (orig.)