The Single Source Concept

When one considers that precursor structure and metal-ligand connectivity determine the composition of nano-matter from a legal perspective, the role of suitable precursors in the designed synthesis of nanomaterials becomes immediately apparent. It is reasonable to assert that solid-state structures can be templated at the nanometer scale by employing well-defined molecular clusters containing metallic elements in a ratio compatible with the targeted ceramic or composite, the so-called SSPs [16-31, 43-51]. The defined metal-ligand interactions in such nano-synthons initiates the growth of nanomaterials at lower temperatures by providing intact nuclei for a bulk material. A large number of different expressions like molecular building blocks, molecular subunits, or modular building units are used to describe metal-organic compounds used as single molecular source.

However, the expression "single-source precursor" is also applied to a mixture of constituents mixed homogeneously either as a powdery mixture (solid) or in a common solvent (liquid) system. While the precursor system in the first case is a physical mixture, the validity of the expression is rather questionable in the second case because it is used to define a precursor cocktail, although no investigations of the nature of the species present in the solution is made, in most of the cases. The use of a mixture of different chemical compounds, corresponding to the elements present in the desired material (e.g., individual Y, Ba, and Cu sources to obtain YBa2Cu3O7-s), complicates the situation in the multiple-precursor route, mainly because of the different chemical nature of the individual chemical species present in the precursor-complex. The composition and phase purity of the material are difficult to control because the intrinsic behaviors of single components, for example, solubility, susceptibility to hydrolysis, etc., in solution-based methods and differential vapor pressures, thermal stability, etc., in the gas-phase synthesis make the stoichiometry highly susceptible to inaccuracies due to an increased number of process variables. In view of the above, the examples described in this article are based on the conversion of defined molecular

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