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Book chapter2014Peer reviewed

Single source precursor approach : Hydrolysis mechanisms in organic media

Kessler, Vadim


In Part I the most important classes of educts, and precursor solutions respectively,used for CSD processing are discussed in detail. For solution synthesis from thedifferent precursors various approaches ranging from simple dissolution of thestarting material in a suitable solvent up to an initial conversion of the startingmaterial into a more soluble or more stable derivative by refluxing and distillationare available. The simple rule “similis similia solvuntur” (like dissolves like), whichwas already known by the alchemists in ancient times, still helps to find a suitablesolvent for the start of the syntheses. Certainly this rudimentary rule gives only thefirst hint for the starting point and optimization has to be performed later on. Thismeans for example that highly polar educts like metal nitrates typically dissolvewell in water, but not in cyclohexane but on the other hand long chain metalcarboxylates such as 2-ethylhexanoates will not dissolve in water or methanol. Inany case the preparation of a “homogeneous” solution including all the necessarycation species that may later be applied to a substrate according to the requirementsenumerated in the corresponding chapters of this book is mandatory. But dissolutionof the educts is not the only issue for the choice of synthesis strategy. One hasalso to consider other aspects like wettability, chemical stability and flowability ofthe resulting precursor solution. Furthermore the requirements of appropriate solubilitycombined with pyrolysis that leaves solely the cations (and oxygen) as aresidue, represent an exceptionally significant limitation regarding the choice ofeducts. Typically, metallo-organic compounds are suitable due to the fact that theirsolubility in polar or non-polar solvents can be tuned by modifying the organic partof the molecule, and because the organic moiety pyrolyzes in oxidizing ambientatmosphere without residue. The synthesized precursor solution must also ensurethat no macroscopic phase separation of precursor components during drying orpyrolysis occurs, i.e. the crystallization of the individual components upon solventevaporation should be avoided and homogeneity at an “atomic” level should beretained.The first two chapters will deal with the educts which are mainly employed forsolution synthesis i.e. simple alkoxides and carboxylates. In Chap. 3 strategies toprepare stable coating solutions from mixtures of these two classes of compoundsas well as precursor solutions containing different metal alkoxides are explained.Then more specific precursor solution approaches, such as the single-sourceprecursors, polymer assisted deposition, and water based precursor solutionapproaches will be described in Chaps. 4–6.It has to be noted that also nitrates and sometimes chlorides (e.g. for indium tinoxide—ITO) have been used for the preparation of precursor solutions, but lessfrequently due to e.g. problems with “micro-explosions”, and the tendency of phaseseparation during drying, because of crystallization of one component. For theintroduction of dopants however metal nitrates can be used due to the low absoluteamount of some mole percent. Halides may cause problems, if they are notcompletely removed during processing and may change the defect chemistry ofthe final oxide.As it becomes clear from this short review of solution synthesis aspects thatexploring new or optimized compositions of (thin film) materials is often tediouswork so that combinatorial synthesis approaches have been adopted from thebiochemistry community. By means of PZT automated synthesis schemes havebeen used to create libraries of compositionally varied mixed oxide thin films frommixable precursor solutions of the end members lead titanate and lead zirconatewith different lead excess. The complementary established automated setup for themeasurement enabled a basic proof of concept. The influence of the kind ofprecursor chemistry on the nucleation and growth of the PZT, as it was found inconventional CSD has not been considered in this technique yet.

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Title: Chemical solution deposition
ISBN: 978-3-211-99310-1
Publisher: Springer

    UKÄ Subject classification

    Materials Chemistry
    Inorganic Chemistry

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