Golubev N V, Ignat'eva E S, Sigaev V N, Lauria A, De Trizio L, Azarbod A, Paleari A, Lorenzi R
P.D. Sarkisov International Laboratory of Glass-based Functional Materials, Mendeleev University of Chemical Technology of Russia, Miusskaya Square 9, 125047 Moscow, Russia.
Phys Chem Chem Phys. 2015 Feb 21;17(7):5141-50. doi: 10.1039/c4cp05485g.
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-Ga2O3 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-Ga2O3 into β-Ga2O3. Differential scanning calorimetry registers an irreversible endothermic process at ∼1300 K, well above the exothermic peak of γ-Ga2O3 nano-crystallization (∼960 K) and below the melting temperature (∼1620 K). Transmission electron microscopy and X-ray diffraction data clarify that glass-embedded γ-Ga2O3 NCs transform into LiGa5O8via diffusion-driven kinetics of Li incorporation into NCs. At the endothermic peak, β-Ga2O3 forms from LiGa5O8 dissociation, following a nucleation-limited kinetics promoted by size-dependent order-disorder change between LiGa5O8 polymorphs. As a result of the changes, modifications of UV-excited NC light emission are registered, with potential interest for applications.
纳米尺度的相变是一个具有挑战性的研究领域，特别是对于固体基质中的纳米晶体（NCs）而言，存在尺寸效应以及与基质的相互作用。在此，我们报告了对碱锗硅酸盐玻璃中γ-Ga2O3 NCs结构演变的研究——这是一个因其发光和紫外到可见光转换而具有技术相关性的体系——结果显示其演变与预期的γ-Ga2O3向β-Ga2O3的转变截然不同。差示扫描量热法记录到在约1300 K处有一个不可逆的吸热过程，远高于γ-Ga2O3纳米晶化的放热峰（约960 K）且低于熔化温度（约1620 K）。透射电子显微镜和X射线衍射数据表明，玻璃包埋的γ-Ga2O3 NCs通过Li掺入NCs的扩散驱动动力学转变为LiGa5O8。在吸热峰处，β-Ga2O3由LiGa5O8解离形成，遵循由LiGa5O8多晶型之间尺寸依赖性有序-无序变化促进的成核限制动力学。这些变化导致了紫外激发的NC发光的改变，在应用方面具有潜在的研究价值。
