From molecules to bismuth oxide-based materials: Potential homo- and heterometallic precursors and model compounds

Bismuth-containing heterometallic oxides are promising candidates for a variety of applications with respect to the microelectronics industry. This is not only because of their physical properties but also as a result of the environmentally benign nature of the bismuth-containing precursors and materials. Bismuth alkoxides, carboxylates and BiPh3 have primarily been used as starting materials in the sol–gel and metal organic vapour deposition (MOCVD) process aimed at the preparation of bismuth oxide-based materials, whereas the interest in bismuth siloxides is more recent. Synthetic and structural aspects of these classes of compounds are discussed in this review. Bismuth alkoxides, siloxides and carboxylates hold potential as starting materials for more sophisticated heterometallic molecular precursors, which have to be developed in order to fully exploit the advantages of modern synthetic strategies that focus on μm and nm-scaled electronic devices and thin films. In this article molecular compounds with potential for the design of heterometallic bismuth oxide-based materials are presented together with feasible applications of the latter. Additionally, a variety of structurally related high-nuclearity molecular bismuth oxo clusters are discussed that serve as model compounds, e.g. for the sol–gel process. The molecular structures of these metal oxo clusters provide insight into the stepwise formation of bismuth oxide following the hydrolysis/polycondensation route. The control over the growth process of metal oxo/hydroxo clusters is a key step in tailoring the morphology and physical properties of the final materials. Recent progress regarding various molecular architectures is presented.