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

Abstract

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 g-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 g-Ga 2 O 3 into b-Ga 2 O 3 . Differential scanning calorimetry registers an irreversible endothermic process at B1300 K, well above the exothermic peak of g-Ga 2 O 3 nano-crystallization (B960 K) and below the melting temperature (B1620 K). Transmission electron microscopy and X-ray diffraction data clarify that glass-embedded g-Ga 2 O 3 NCs transform into LiGa 5 O 8 via diffusion-driven kinetics of Li incorporation into NCs. At the endothermic peak, b-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.

Donor–Acceptor Control in Grown‐in‐Glass Gallium Oxide Nanocrystals by Crystallization‐driven Heterovalent Doping

“…In agreement with other studies on similar compositions, the exothermic peak is related to the process of nanocrystallization of γ‐Ga 2 O 3 in the glass matrix, whereas the endothermic peak is caused by NC decomposition after transformation into LiGa 5 O 8 by Li diffusion, with final formation of β‐Ga 2 O 3 NCs. Besides these shared features, the DSC curves of both Ni and Ti‐doped samples show some differences from the curve of the undoped composition, consisting of small but clear shifts of the glass transition temperature T g (Figure a) and of the exothermic and endothermic peaks at T exo and T endo (Figure b and Figure c).…”

“…We know, in fact, that the temperature of the endothermic process at about 1000 °C mainly depends on the final LiGa 5 O 8 NC size, which results from mechanisms of NC coalescence and Li embedding, occurring at temperatures above T exo . Specifically, the larger the NC size, the higher the temperature of the endothermic peak.…”

“…We know,i nf act, that the temperature of the endothermic process at about 1000 8Cm ainly dependso nt he final LiGa 5 O 8 NC size, which resultsf rom mechanismso fN Cc oalescence and Li embedding, occurring at temperatures above T exo . [46] Specifically,t he larger the NC size, the highert he temperature of the endothermic peak. As NC coalescence and Li diffusion are promoted by viscosity lowering, the higher the dopingwith lower glass viscosity-the larger the size of LiGa 5 O 8 NCs.…”

Pre-crystallization heat treatment and infrared luminescence enhancement in Ni2+-doped transparent glass-ceramics

“…2f). This result is consistent with the fact that Li ions can diffuse from the glass matrix into γ-Ga 2 O 3 NCs to form LiGa 5 O 8 [32]. Therefore, γ- (Fig.…”

Synthesis and structural characterization of gallium oxide powders

“…They explored that the ultrathin gallium oxide layers could be a promising candidate for protective layers in flexible organic (opto-) electronics and photovoltaics due to permeation barrier functionalities in conjunction with high optical transparency [9]. In addition, Golubev and his co-workers investigated the diffusion-driven and sizedependent phase changes of gallium oxide nanocrystals in a glassy host [10]. Cai and his co-workers investigated the capacitive behavior of single gallium oxide nano belt [11].…”