Prereacted precursor

The use of a prereacted precursor is the typical approach to the preparation of ceramics of the Tl-containing superconductors (S). For example, to prepare the 120K T1 phase, H2Ba2Ca2CusO10, or 2223-T1, an alkaline earth cuprate precursor which is a mixed phase sample of overall stoichiometry, Ba2Ca2CusOx is prepared by standard ceramic techniques. An intimate mixture of the precursor and a stoichiometric... 

In attempts to reduce toxic hazards, eliminate homogeneous prereactions, lower deposition temperatures, and use cheaper precursors there have been considerable efforts directed toward the development of alternative precursors for use in MOCVD.10 Another approach to using intrinsically less reactive compounds is to use a single-molecule (or single-source ) precursor, in which all the elements required in the film are present in the one molecular species. The compounds potentially exhibit many or all of the following advantages over conventional MOCVD precursors ... 

The fifth contribution by M. Putkonen and L. NiinistO presents an overview of Organometallic Precursors for Atomic Layer Deposition (ALD). The key principle of ALD in contrast to CVD is the exclusion of any gas-phase prereaction allowing the thin film growth to be fully controlled by surface reactions and adsorption/desorption kinetics. ALD is thus ideally suited for the growth of ultra-thin layers and atomically abrupt interfaces needed in future nanoelectronic devices. While CVD and ALD have many aspects in common, precursors suitable for ALD generally need to be much more reactive than those used for CVD. Another challenge is to combine low steric demand with very high selectivity of the surface reactions. 

Nd-precursors. These additives comprise alcohols, organic acids, esters of organic acids, lactones of organic acids, tributyl phosphate, tripenylphosphin, diethyl phosphinoethane, diphenyl phosphinoethane, acetylacetonate, tri-ethylamine, AbN -dimclhyl acetoamide, tetrahydrofuran, diphenylether etc. In this context alkyl aluminum chloride which is prereacted with TBP is worth mentioning [386,387]. 

The most common technique used to prepare the /i-type (i.e., or / ") alumina is to mechanically blend the component oxides or precursor compounds in powder form prior to a calcination or prereaction step at temperatures between 1000 and 1260°CT Commercially available aluminum oxide powders (0.3-0.5 pm average crystallite size) in the alpha (corundum) polymorph are typically usedT They are derived from three common sources decomposition of gibbsite [Al(OH)3], which is precipitated from soda liquors in the Bayer process preparation and decomposition of alum salts and preparation from aluminum chloride precursors NaaCOs is usually the source of Na20. Sources of Li20 have included Li2C03, LiNOs, and Li2C204- MgO is usually added as the commercially available oxide. 

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