Controlling the Mechanism of Phase Transformation of Colloidal In₂O₃ Nanocrystals

Abstract

Controlling the crystal structure of transparent metal oxides is essential for tailoring the properties of these polymorphic materials to specific applications. The structural control is usually done via solid state phase transformation at high temperature or pressure. Here, we report the kinetic study of in situ phase transformation of In2O3 nanocrystals from metastable rhombohedral phase to stable cubic phase during their colloidal synthesis. By examining the phase content as a function of time using the model fitting approach, we identified two distinct coexisting mechanisms, surface and interface nucleation. It is shown that the mechanism of phase transformation can be controlled systematically through modulation of temperature and precursor to solvent ratio. The increase in both of these parameters leads to gradual change from surface to interface nucleation, which is associated with the increased probability of nanocrystal contact formation in the solution phase. The activation energy for surface nucleation is found to be 144 ± 30 kJ/mol, very similar to that for interface nucleation. Despite the comparable activation energy, interface nucleation dominates at higher temperatures due to increased nanocrystal interactions. The results of this work demonstrate enhanced control over polymorphic nanocrystal systems and contribute to further understanding of the kinetic processes at the nanoscale, including nucleation, crystallization, and biomineralization.

Effects of a More Accurate Polarizable Hamiltonian on Polymorph Free Energies Computed Efficiently by Reweighting Point-Charge Potentials

“…Predicting all of the potentially stable crystal structures is of particular interest to the pharmaceutical industry, where the presence of a more stable polymorph can render commercial drugs ineffective and lead to costly market recalls. [1][2][3][4][5][6][7][8] The influence of polymorphism in commercial materials is not limited to pharmaceutical applications and has been observed to affect the hydraulic properties of cement, 9 the reactivity of energetic materials, 10-13 the weather resistance of dyes, 14 the transparency of optical photonics materials 15,16 and the charge carrier mobility in semi-conductor materials. [17][18][19][20][21] Computer-based models can, in principle, rapidly and inexpensively take a particular molecule as input and search through possible crystal structures, identifying the set of stable or metastable polymorphs which are likely to be observed experimentally.…”

Diffusion-driven and size-dependent phase changes of gallium oxide nanocrystals in a glassy host

“…The detailed mechanisms underlying structural phase changes at the nanoscale are not easily predictable in general, 8,9 and particularly when the process involves NCs interacting with a solid host. [10][11][12][13] This is the case of Ga oxide NCs in silicate glass, which is one of the prototypal systems of oxide-in-oxide nanostructured glasses together with SnO 2 -doped silica.…”

Defects and impurities in colloidal Ga2O3 nanocrystals: new opportunities for photonics and lighting

“…5 nm for In 2 O 3 ). 5,[45][46][47] This phenomenon has been associated with surface energy and surface stress effects, which can become dominant contributions to the phase stabilization Gibbs free energy when surface-to-volume ratio of NCs is sufficiently large. In comparison to β phase, γ-Ga 2 O 3 has been much less investigated.…”