NEW AURIVILLIUS-RELATED PHASES IN THE SB-(W,V)-O SYSTEM - STRUCTURAL STUDY AND PROPERTIES

摘要

Two types of solid solutions (Sb2W1-xVxO6-x with x up to 0.5 and Sb2W1-yVyO6-y/2 with y up to 0.4) have been obtained by substitution of W(VI) with V(IV) or V(V) in Sb2WO6. These materials have been studied by X-ray powder diffraction methods, showing a gradual evolution of the unit cell parameters according to the ionic radii of the different cations, as well as the appearance of oxygen vacancies in the network. Crystal growth of these phases has been carried out, and a single-crystal structure determination has been performed on a sample corresponding to the formula Sb2W0.75V0.25O5.75. This material crystallizes in the monoclinic system, space group P2(1)/a, with unit cell parameters a = 5.529(3), b = 4.914(2), c = 9.193(5)Angstrom and beta = 96.04(4)degrees, and has been refined down to R = 0.067. The structure is related to the classical Aurivillius framework, being built up by alternating infinite [Sb-O] sheets,vith [(W,V)-O] layers, which include the oxygen vacancies. Impedance measurements were carried out on two representative Sb2W0.75V0.25O5.75 [V(IV)] and Sb2W0.75V0.25O5.875 [V(V)] samples. In both cases the electrical response is dominated by an electronic conductivity that is higher for the V(IV) (Sb2W0.75V0.25O5.75) compound. (C) 1997 Academic Press. [References: 36]