STRUCTURAL EVOLUTION OF THE AURIVILLIUS FRAMEWORK IN THE SOLID-SOLUTIONS BI2WO6-SB2WO6

The existence of two solid solutions of Bi2-xSbxWO6 composition is demonstrated, the first one isostructural with the ferroelectric Bi2WO6 oxide (SSB, 0 less than or equal to x less than or equal to 1.25), and the second one (SSS, 1.5 less than or equal to x less than or equal to 2) isostructural with the ferroelastic Sb2WO6 compound. Both structures keep the basic framework of Aurivillius oxides, but the study of the structural evolution with x in SSB phases shows the progressive distortion of Bi2WO6 prototype network, that can be related to their possible ferroelectric behavior. The Bi-O-2-Bi arrangement of Bi2O2 layers for x=O transforms to Bi,Sb-O-O-Bi,Sb for x>O, being the interspace region between oxygen sheets, along [001] direction, larger for larger x values. This fact is correlated to the less stereochemical activity of 6s(2) lone pair of electrons of Bi3+ relative to the 5S(2) electrons of Sb3+ cation. The SSB orthorhombic structure remains until such (Bi,Sb)(2)O-2 modification cannot be assumed by the framework, leading to the SSS triclinic structure.