Structural study of modified Bi4V2O10+delta phases (delta=0.0.5,1) influence of antimony contribution

Three solid solutions of general composition Bi4-xSbxV2O10, Bi4V2-y4+Vy5+O1 0+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 diff raction and electron microscopy techniques. Single phases have been isolate d 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 str uctures determined by X-ray diffraction methods. The three oxides crystalli ze in the orthorhombic system, space groups F222, Amam, and Fmmm, respectiv ely. Their structures keep the classical two-dimensional array of Aurivilli us-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 5s(2) lone pair associated with Sb3+ and 6s(2) 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 o ctahedra for V4+ and V5+, and octahedra for Sb5+. This fact can be related to the electrical properties, such as high ionic conduction and ferroelectr icity, shown by these types of materials. (C) 1999 Academic Press.