Synthesis, structural and microstructural study of Bi4W0.5Ti0.5O8X (X=Cl, Br) Sillén-Aurivillius intergrowths

Bi4W0.5Ti0.5O8X oxyhalides were synthesised for X=Cl, Br with orthorhombic unit cell parameters a=5.439(4)Å, b=5.468(7)Å, c=14.190(9)Å (S.G. Cm2m no 38) and a=5.468(3)Å, b=5.502(5)Å and c=28.809(9)Å (S.G. Ic2m no 46) respectively. These compounds can be described as a regular intergrowth of the simplest members of Sillén and Aurivillius phases. The structural features of these compounds were determined by means of transmission electron microscopy and associated techniques and powder X-ray diffraction. Electron diffraction shows clearly the structural defects produced by the bromine substitution and high-resolution images reveal the presence of stacking defects as well.