Structural study of Ba11Fe8Ti9O41 by X-ray diffraction

The crystal structure of Ba11Fe8Ti9O41 was determined using single crystal and powder X-ray diffraction methods. This new phase crystallizes in the hexagonal space group P6(3)/mmc (No 194) (a=5.7506(3) Angstrom, c=61.413(2) Angstrom; Z=2; rho(calc) = 5.75 g cm(-3)) and exhibits a 26-layer structure built from close-packed {[}O,(Ba,O)] layers with a stacking sequence (chcchchchcchc)(2). Octahedral sites are occupied by a mixture of Fe3+ and Ti4+, with some preferential ordering of the Fe ions, and tetrahedral sites are occupied by Fe3+. The magnetic Fe ions were observed to concentrate within four contiguous cp layers around z=1/4 and 3/4. Unusual structural features, including cation disorder associated with unreasonably short cation-cation separations, were observed to occur within these magnetic sections of the structure. Indexed X-ray powder diffraction data for polycrystalline Ba11Fe8Ti9O41 are given. Complementary structural studies of this compound using neutron and electron diffraction are underway and will be described elsewhere along with the results of dielectric and magnetic property measurements. (C) 2000 Editions scientifiques et medicales Elsevier SAS. All rights reserved.