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

Phase transformations at the nanoscale represent a challenging field of research, mainly in the case of nanocrystals (NCs) in a solid host, with size-effects and interactions with the matrix. Here we report the study of the structural evolution of γ-Ga 2 O 3 NCs in alkali-germanosilicate glass - a t...

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Bibliographic Details
Published in:Physical chemistry chemical physics : PCCP 2015-01, Vol.17 (7), p.5141-515
Main Authors: Golubev, N. V, Ignat'eva, E. S, Sigaev, V. N, Lauria, A, De Trizio, L, Azarbod, A, Paleari, A, Lorenzi, R
Format: Article
Language:English
Subjects:
Endothermic reactions
Evolution
Light emission
Lithium
Nanocrystals
Nanostructure
Order disorder
Phase transformations
Transformations
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Summary:Phase transformations at the nanoscale represent a challenging field of research, mainly in the case of nanocrystals (NCs) in a solid host, with size-effects and interactions with the matrix. Here we report the study of the structural evolution of γ-Ga 2 O 3 NCs in alkali-germanosilicate glass - a technologically relevant system for its light emission and UV-to-visible conversion - showing an evolution drastically different from the expected transformation of γ-Ga 2 O 3 into β-Ga 2 O 3 . Differential scanning calorimetry registers an irreversible endothermic process at ∼1300 K, well above the exothermic peak of γ-Ga 2 O 3 nano-crystallization (∼960 K) and below the melting temperature (∼1620 K). Transmission electron microscopy and X-ray diffraction data clarify that glass-embedded γ-Ga 2 O 3 NCs transform into LiGa 5 O 8 via diffusion-driven kinetics of Li incorporation into NCs. At the endothermic peak, β-Ga 2 O 3 forms from LiGa 5 O 8 dissociation, following a nucleation-limited kinetics promoted by size-dependent order-disorder change between LiGa 5 O 8 polymorphs. As a result of the changes, modifications of UV-excited NC light emission are registered, with potential interest for applications. We describe the evolution of γ-Ga 2 O 3 nanocrystals in alkali-germanosilicate glass, disclosing mechanisms of nanocrystal-matrix interaction via a diffusion-driven change, into LiGa 5 O 8 and β-Ga 2 O 3 formation by decomposition promoted by size-dependent order-disorder polymorphism.
ISSN:1463-9076
1463-9084
DOI:10.1039/c4cp05485g