Precursor design

Conversely, since a great many routes for precursor design are now known, improvements in the control of polymerization reactions will be essential. Studies should be directed to the accurate measurement of the molecular weights, Mn and Mw, of the inorganic polymers by using size-exclusion chromatography techniques. 

Clearly the full potential of CIS PV devices has not been fully exploited, since the combination of group I-III-VI2 elements can result in a variety of end products. Therefore, standards need to be defined that can associate device processing, fabrication, and film composition to cell band gap and efficiency. Spray CVD in conjunction with SSP design provides a proof-of-concept for a reproducible highly manufacturable process. Items that need more investigation include (1) precursor design development of more volatile/thermally... 

We have developed a process to make metastable materials by rapid solidification (7) and have applied it to various alloy systems (8). There were few reports on such a metastable processing to make precursors for Raney catalyst. The metastable processes maybe extend the probability of precursor design by decreasing the limit of additive amount to precursor. 

These last two points concern how precursor design and synthesis are influenced by the precursor-to-ceramic conversion process. The next set of criteria identify materials properties that drive precursor design and synthesis including product selectivity. 

Chemical and phase purity are critical issues that drive precursor design because optimal mechanical properties are achieved only with high purity. For example, ceramics grade Nicalon fibers, with a chemical composition of ca SiCi 45O0 36 and densities 17,9... 

Method development, based on past precedents (bottom-up/top-dovim, precursor design, synthetic pathvirays, choice of solvents, theoretical calculations, etc.)... 

Figure 4.44. Synthetic pathway for single-source precursor design. Reproduced with permission from Inorg. Chem. 2003, 42, 7713. Copyright 2003 American Chemical Society.

Whereas plants and certain microorganisms can generate all required coenzymes from CO2 or simple organic precursors, animals must obtain precursors (designated as vitamins) for a major fraction of their coenzymes from nutritional sources. Still, most vitamins must be converted into the actual coenzymes by reactions catalyzed by animal enzymes. The structures and biosynthetic pathways of some coenzymes are characterized by extraordinary complexity. Enzymes for coenzyme biosynthesis have frequently low catalytic rates, and some of them catalyze reactions with highly unusual mechanisms. 

Given the implications of molecular level processing, the molecules-to-materials rationale has been successfully applied to various material compositions.However, the viability of precursor design with respect to material composition is rather vulnerable because the correlation between the starting entities and the final products is poorly understood. Nevertheless, recent chemical approaches have yielded materials designed to have predetermined structures, compositions, and properties, providing proof-of-principle for new concepts. Therefore, this chapter mainly focuses on the conceptual advancements in synthesis and application of molecular precursors in the preparation of inorganic materials. 

Figure 6 Possible metal combinations in heterocubanes of general formula [ flexibility of precursor design." Reproduced with permission from Wiley.

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