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 ≤ x ≤ 1.25), and the second one (SSS, 1.5 ≤ x ≤ 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-O2-Bi arrangement of Bi2O2 layers for x = 0 transforms to Bi,Sb-O-O-Bi,Sb for x > 0, 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 6s2 lone pair of electrons of Bi3+ relative to the 5s2 electrons of Sb3+ cation. The SSB orthorhombic structure remains until such (Bi,Sb)2O2 modification cannot be assumed by the framework, leading to the SSS triclinic structure.