Solution-precursor-solid mechanism

Among the three polymorphs of crystalline calciiun carbonate, calcite is the equilibrium phase, most commonly adopting a rhombohedral morphology. In biologically produced minerals, however, the rhombohedral morphology is rarely adopted. Single-crystalline calcite fibers are observed most prominently in sea-urchin teeth and bacterial deposits [67-69]. They do not follow the crystallographic symmetry of calcite. Such calcite fibers were prepared in vitro via a solution-precursor-solid mechanism [70]. 

Organometallic precursors were also used for the preparation of III-V semiconductors. Buhro reported the use of a single-source precursor Bu 2ln[/t-P(SiMe3)2] 2, which upon methanolysis in toluene leads to a mixture of InP and In nanoparticles, which promote the growth of InP fibers through a solution-liquid-solid mechanism. " ... 

Solution-Liquid-Solid (SLS) growth of semiconductor nanowires by Wang etal. (2006). The synthesis proceeds by a solution-based catalysed growth mechanism in which nanometer-scale metallic droplets catalyse the decomposition of metallo-organic precursors and crystalline nanowire growth. 

Without the assumption of any nucleation mechanism we could already distinguish three characteristic regimes after the addition of alkaline LiOH an ethanolic zinc acetate precursor solution (vertical solid line between region (I) and region (II)) ... 

A method to circumvent the problem of chalcogen excess in the solid is to employ low oxidation state precursors in solution, so that the above collateral reactions will not be in favor thermodynamically. Complexation strategies have been used for this purpose [1, 2]. The most established procedure utilizes thiosulfate or selenosulfate ions in aqueous alkaline solutions, as sulfur and selenium precursors, respectively (there is no analogue telluro-complex). The mechanism of deposition in such solutions has been demonstrated primarily from the viewpoint of chemical rather than electrochemical processes (see Sect. 3.3.1). Facts about the (electro)chemistry of thiosulfate will be addressed in following sections for sulfide compounds (mainly CdS). Well documented is the specific redox and solution chemistry involved in the formulation of selenosulfate plating baths and related deposition results [11, 12]. It is convenient to consider some elements of this chemistry in the present section. 

All the solid phases were identified and characterized for crystallinity by X-ray powder diffraction (Philips PW 1730/10 diffractometer, Cu Kq radiation equipped with a PW 1030/70 vertical goniometer and connected to a P.C. computer for quantitative analyses). Crystallinities for Nu-10 and cristobalite were computed by comparing the intensity of the most characteristic diffraction peaks of each sample to that of the corresponding pure 100% crystalline phases used as standards. In some cases calibration curves derived from Nu-10/cristobalite mechanical mixtures were used. Si, Al, and alkali contents were determined either on precursors or calcined samples (900 C, air flow, 4h) by atomic absorption, using a Perkin-Elmer 380 AA instrument after digestion and dissolution of the samples in H,S04/HF solutions and further elimination of HF by gentle heating at 60 C for 12 n. 

Recent studies have demonstrated that the chemical homogeneity of the freeze-dried precursor in many cases has no decisive influence on its thermolysis mechanism. It is well known that thermal decomposition of solid solutions of salts can lead to the formation of individual oxides instead of complex oxide compounds. Similar phenomena were observed during thermal decomposition of amorphous freeze-dried precursors in spite of their high chemical homogeneity. " Meanwhile, the small grain size of thermolysis products and their high reactivity resulted in the fast synthesis of complex oxides soon after thermal... 

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