Nucleation and growth of magnetite from solution

Abstract

The formation of crystalline materials from solution is usually described by the nucleation and growth theory, where atoms or molecules are assumed to assemble directly from solution. For numerous systems, the formation of the thermodynamically stable crystalline phase is additionally preceded by metastable intermediates . More complex pathways have recently been proposed, such as aggregational processes of nanoparticle precursors or pre-nucleation clusters, which seem to contradict the classical theory. Here we show by cryogenic transmission electron microscopy that the nucleation and growth of magnetite-a magnetic iron oxide with numerous bio- and nanotechnological applications-proceed through rapid agglomeration of nanometric primary particles and that in contrast to the nucleation of other minerals, no intermediate amorphous bulk precursor phase is involved. We also demonstrate that these observations can be described within the framework of classical nucleation theory.

Phase-transition-driven growth of compound semiconductor crystals from ordered metastable nanorods

“…7d). Consequently, the rate of volume growth can be expected to be proportional to its surface, which corresponds to normal grain growth [49]. According to this model, the transition from nanorods to larger grains and the phase transition from wurtzite to kesterite occur simultaneously, which is in excellent agreement with the real-time analysis (Fig.…”

Crystallizing Elusive Chromium Polycations

“…Removal of nitrate by evaporation of the HNO3-H2O azeotrope drives cluster formation only as a crystalline solid. This 'classical' growth mechanism, a description of metal oxide formation without polynuclear cluster assembly prior to crystallization, bypasses the unstable solution cluster state that usually results in aggregation and production of an insoluble hydroxide (Baumgartner et al, 2013;Gebauer et al, 2014;Gebauer et al, 2008;Habraken et al, 2013). Crystallization of clusters without initial persistence in solution has not previously been considered as a way to isolate highly reactive clusters.…”

Magnetic properties of polycrystalline cobalt nanoparticles

“…It seems that this numerical model may adequately describe the distribution of the easy anisotropy axes in real polycrystalline nanoparticles created as a result of the coalescence of small monocrystalline embryos originally formed by a chemical reaction in a solution. 22 Fig. 1a shows the energy diagram of stationary micromagnetic states in single-crystal and polycrystalline spherical cobalt nanoparticles.…”

“…Now it is well established by means of HRTEM analysis [22][23][24][25][26] that despite their small dimensions, a magnetic nanoparticle may have a complex microstructure. It can often be represented as a dense agglomeration of monocrystalline granules of different sizes having different orientations of the crystal lattice with respect to each other.…”