Nanostructured Bimetallic Oxide Ion-Conducting Ceramics from Single-Source Molecular Precursors

Abstract

A new approach for the formation of bimetallic coordination complexes of bismuth containing a 1:1 ratio of the two metal species has been developed. The strategy exploits the Lewis acidic nature of bismuth and has been used to synthesize the new complexes BiV(O)(Hsal)(sal)(salen*)·CH2Cl2 (1), BiCu(Hsal)3(salen) (2), and BiNi(Hsal)3(salen)·CH2Cl2 (3) (salen = ethylenebis(salicylimine), salen* = ethylenebis(3-methoxysalicylimine), sal = O2CC6H4-2-O, Hsal = O2CC6H4-2-OH). The compounds have been characterized spectroscopically and, in the case of 2 and 3, by single-crystal X-ray diffraction. The decomposition of the bimetallic complexes by both thermal and hydrolytic routes has been investigated. The ability of the compounds to act as single-source precursors for the formation of bimetallic oxides has been explored. Oxide ion-conducting phases have been produced by direct pyrolysis of 1, which results in the formation of monoclinic BiVO4, and by pyrolysis of mixtures of 1 and 2 or 3, which results in isolation of the γ‘-related Bi2VxM1-xO5.5-δ (M = Cu, Ni). Thermal decomposition of the molecular compounds results in the formation of spherical oxide nanoparticles with diameters ranging from approximately 110 nm to 1 μm. Hydrolytic decomposition of the complexes results in the formation of nanoparticles with an average diameter of 40 nm. The materials produced in this manner have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and powder X-ray diffraction. Conservation of metal stoichiometry in converting the molecular precursor to the corresponding oxide has been confirmed by analysis of the materials by energy-dispersive X-ray spectroscopy.