Refinement of the structures of two layered cationic conductors

The neutron powder diffraction and local bond valence balance methods were used to refine the related monoclinic structures of Na4.4Fe0.4Ti4.6O12 (spa ce group C2/m, a = 26.5176(9) Angstrom, b = 2.9484(1) Angstrom, c = 6.3225( 2) Angstrom, beta = 95.808(1)degrees) and Na4+2x-yMgxTi6-xO14-yFy (space gr oup P2/m, a = 15.8137(6) Angstrom, b = 2.9643(1) Angstrom, c = 6.2908(2) An gstrom, beta = 99.8361(1)degrees). The sites of heterovalent substituents ( Fe, Mg, F) and sodium site occupancies were;determined. The geometry and to pology of sodium migration channels (passage radii, interstitial cavities, jump lengths, connectivity) were analyzed. Wide passages were shown to run only in one direction, despite the layered character of the structures.