Use of Precession Electron and X Powder for solution and refinement of materials

This communication will present the case study of ALa5O5(VO4)2 (A= Li, Na, K, Rb), example of the use of a combination of Precession Electron and X-ray Powder Data for the solution and the refinement of new materials. Indeed, an original structural type has been evidenced in the system (A, La, V, O) with A=Li, Na, K, Rb. Attempts to solve the structure ab initio on X-ray powder data were unsuccessful (more particularly because the powder was a mixture of the title compound and of unreacted precursors). The structure was finally solved by charge flipping using Precession Electron Data (3D tomography) on a nanocrystal, enabling a posteriori the good formulation of a pure powder. This powder was then classically refined by Rietveld method showing the correctness of the electron-solved structure. It crystallizes in a monoclinic unit cell with space group C2/m and a=20.2282(14) b=5.8639(4) c=12.6060(9) Å and β=117.64(1)⁰. The ALa5O5(VO4)2 structure is built of (OLa4) tetrahedral units creating Crenel-like 2D ribbons. These ribbons, surrounded by four isolated VO4 tetrahedra, are creating channels parallel to b axis in which A+ ions are located.