Studies on n=2 Aurivillius phases: structure of the series Bi3−xLaxTiNbO9 (0≤x≤1)

The crystal structures of the solid solutions of Bi3−xLaxTiNbO9 (0≤x≤1) have been analyzed by powder X-ray diffraction with supporting evidence from selected area electron diffraction (SAD). The structure of the starting member (x=0) is verified to be in the orthorhombic space group A21am while the end member (x=1) is determined to crystallize in the centrosymmetric orthorhombic space group Pmcb. The structure of x=1 phase is solved by ab initio powder diffraction. The intermediate compositions belong to the space group A21am as confirmed by Rietveld refinements. Rietveld refinements on all the compositions reveal that the La3+ ion is disordered only in the A site and not in the [Bi2O2]2+ layer. The tilt in the Ti/NbO6 octahedra decreases with increasing x.