posted on 2007-01-23, 00:00authored byDavid Ávila-Brande, Ángel R. Landa-Cánovas, L. Carlos Otero-Díaz
During the synthesis of the compound with nominal composition Bi4Cu1/3W2/3O7.8Cl, a new family of
compounds, which can be described as ordered intergrowth of one Sillén block [Bi2O2Cl] and n oxygen
deficient blocks [Bi2Cu1/(2n+1)W2n/(2n+1)O6-δ]n with δ = 0.18, was produced. Transmission electron
microscopy and associated techniques were used to determine the composition, unit-cell symmetry, and
space group of the main phase corresponding to the n = 1 member Bi4Cu1/3W2/3O8-δCl. Structural models
for both compounds n = 1 and n = 2 were deduced by exit wave reconstruction in a crystal where these
phases were intergrown. The existence of the highest members n = 3 and 4 was confirmed by HREM
in several crystallites, in which we have found the compounds with n = 1−4 as disordered intergrowths.
Moreover, some crystals with cationic ordering in the octahedral layer were also found. Oxygen atoms
and vacancies were imaged using the exit wave reconstruction technique in the structure determination
of the first Sillén-BICUWOX intergrowth. The average structure of the main phase Bi4Cu1/3W2/3O8-δCl
was refined from X-ray powder diffraction data using the Rietveld method, yielding a tetragonal unit
cell with lattice parameters a = 3.845(9) Å, c = 14.188(7) Å (space group P4/mmm No. 123), which
could be described as a Sillén−Aurivillius oxygen deficient intergrowth.