Nanostructured Bimetallic Oxide Ion-Conducting\nCeramics from Single-Source Molecular Precursors

Abstract

A new approach for the formation of bimetallic coordination complexes of bismuth\ncontaining a 1:1 ratio of the two metal species has been developed. The strategy exploits\nthe Lewis acidic nature of bismuth and has been used to synthesize the new complexes\nBiV(O)(Hsal)(sal)(salen*)·CH₂Cl₂ (<b>1</b>), BiCu(Hsal)₃(salen) (<b>2</b>), and BiNi(Hsal)₃(salen)·CH₂Cl₂ (<b>3</b>) (salen = ethylenebis(salicylimine), salen* = ethylenebis(3-methoxysalicylimine), sal\n= O₂CC₆H₄-2-O, Hsal = O₂CC₆H₄-2-OH). The compounds have been characterized spectroscopically and, in the case of <b>2 </b>and<b> 3</b>, by single-crystal X-ray diffraction. The decomposition\nof the bimetallic complexes by both thermal and hydrolytic routes has been investigated.\nThe ability of the compounds to act as single-source precursors for the formation of bimetallic\noxides has been explored. Oxide ion-conducting phases have been produced by direct pyrolysis\nof <b>1</b>, which results in the formation of monoclinic BiVO₄, and by pyrolysis of mixtures of <b>1</b>\nand <b>2</b> or <b>3</b>, which results in isolation of the γ‘-related Bi₂V<i>_x</i>M₁_-<i>_x</i>O_5.5_-_δ (M = Cu, Ni). Thermal\ndecomposition of the molecular compounds results in the formation of spherical oxide\nnanoparticles with diameters ranging from approximately 110 nm to 1 μm. Hydrolytic\ndecomposition of the complexes results in the formation of nanoparticles with an average\ndiameter of 40 nm. The materials produced in this manner have been characterized by\nscanning electron microscopy (SEM), transmission electron microscopy (TEM), and powder\nX-ray diffraction. Conservation of metal stoichiometry in converting the molecular precursor\nto the corresponding oxide has been confirmed by analysis of the materials by energy-dispersive X-ray spectroscopy.