Structural study of modified Bi4V2O10+δ phases (δ = 0, 0.5, 1): Influence of antimony contribution

Three solid solutions of general composition Bi4-xSbxV2O10, Bi4V2-y4+Vy5+O10+y/2, and Bi4V2-zSbzO11 have been investigated in the fivefold Bi2O3-V2O5-V2O4-Sb2O3-Sb2O5 system. These oxides have been characterized by X-ray diffraction and electron microscopy techniques. Single phases have been isolated for values ranging from 0 to x, z = 0.8 and y = 2. Single crystals of Bi3.2Sb0.8V2O10, Bi4V2O10.5, and Bi4V1.2Sb0.8O11 have been grown and their structures determined by X-ray diffraction methods. The three oxides crystallize in the orthorhombic system, space groups F222, Amam, and Fmmm, respectively. Their structures keep the classical two-dimensional array of Aurivillius-like oxides with (Bi, Sb)-O layers interleaved with (V, Sb)-O sheets. It has been found that Sb3+ is introduced into the bismuth layer, due to its similar sterical behavior, by the presence of a 5s2 lone pair associated with Sb3+ and 6s2 associated with Bi3+, whereas Sb5+ substitutes for the V5+ cation. All of the substitutions carried out mainly act on the vanadium layer, which can accommodate different coordination polyhedra for cations: tetrahedra for V5+, square pyramids and distorted trigonal bipyramids or octahedra for V4+ and V5+, and octahedra for Sb5+. This fact can be related to the electrical properties, such as high ionic conduction and ferroelectricity, shown by these types of materials