Nanoscale composition fluctuations and crystallization process: Case study in Li₂O–SiO₂‐based glasses

Abstract

Nanoscale composition fluctuations in Li2O–SiO2‐based glasses were analyzed and discussed from the data on the structure and crystallization process reported so far to enter deeply into the medium‐range ordered structure of multicomponent oxide glasses. Li2O is proposed to have a strong tendency for dynamical heterogeneous structure, that is, the formation of fragile Li2O‐rich regions with small SiO2 contents, resulting in the initial crystallization of metastable Li2SiO3 prior to the formation of stable Li2Si2O5 in Li2O–2SiO2‐based glasses. Li2O–Ga2O3/Nb2O5–SiO2 glasses are proposed to have nanoscale composition fluctuations of Li2O–Ga2O3/Nb2O5‐rich regions, resulting in the initial formation of LiGa5O8 and LiNbO3 nanocrystals. In Li2O–Al2O3–SiO2 glasses, the distribution width of composition fluctuations is proposed to be narrow, resulting in the initial crystallization of metastable β‐quartz solid solutions Li2O·Al2O3·nSiO2 (n = 6–8). Additive P2O5 and NiO leading to an enhanced nucleation are proposed to be present in fragile Li2O‐rich regions.

A new perspective for nucleation and nanocrystallization from interfacial energy and nanoscale composition fluctuations in glasses

“…Nowadays, the existence of spatially and compositionally heterogeneous structures in multicomponent oxide glasses has been well established through experiments and simulations 17–27 . The present authors’ group 28–32 extended the fragility concept proposed by Angell 33,34 to local composition fluctuations in multicomponent oxide glasses, that is, the DNCF model. That is, multicomponent oxide glasses consist of nanoscale network former‐rich strong region and nanoscale network modifier‐rich fragile region and nucleation is initiated preferentially in the nanoscale fragile region.…”

“…On the other hand, the “nonstoichiometric composition” being the composition deviated from the formed (target) crystalline phase is also used to control viscosity and thermal properties of the base glasses and to design the microstructure of glass‐ceramics. For a stoichiometric glass, a narrow distribution in nanoscale composition fluctuations would be created, whereas a broad distribution would be created for nonstoichiometric glasses 28,31 . Basically, in the crystallization of a stoichiometric glass, the target (stoichiometric) crystalline phase would be formed predominantly, whereas in the crystallization of a nonstoichiometric glass, the formation of not only the target crystalline phase but also other crystalline phases would be induced.…”

“…On the other hand, the MRO structure in glasses is related to the linkage style of SRO structural units and is characterized by “density fluctuations” and “composition fluctuations” at nanoscale levels, that is, “nanoscale heterogeneous structures.” 17–27 Nowadays, it is very important to clarify concretely the nanoscale heterogeneous structure, for example, their chemical composition, fraction, and connectivity, in a given glass. Recently, the present authors’ group 28–32 tried to explain the nucleation process and crystallization sequence (the formation order of crystalline phases) in various multicomponent oxide glasses by using the model of the distribution of nanoscale composition fluctuations (DNCF) and the concept of Ostwald's step rule (rule of stages).…”

In Situ Formation of Li2SiO3-Li-NaCl Interface on Si and Its Effect on Hydrogen Evolution

“…33 The Li x SiO y phase is attributed to the product formed from the reaction of LiOH and SiO 2 . Moreover, a spot of SiO 2 would attach to the surface in the form of Li 2 O•nSiO 2 sediments during the initial hydrolysis stage with a low SiO 2 concentration, 34 so that the Li 1s peak of Li 2 O can be also observed. When the reaction extends to 3.0 h, the content of Li x SiO y keeps growing, which is consistent with the continuous consumption of LiOH along with the real-time decrease in the pH value (Figure 5d).…”

From nanoscale heterogeneities to nanolites: cation clustering in glasses

“…In Molecular Dynamics simulations of CaO-Al 2 O 3 -SiO 2 glasses, dynamical heterogeneities have been identified with compositional and structural fluctuations associated with regions enriched with CaO and Al 2 O 3 (high mobility) or SiO 2 (low mobility) [10]. Over the last 10 years, the importance of nanoscale heterogeneities has been increasingly recognized due to the emergence of new techniques, notably by directly imaging the spatial and chemical fluctuations using Transmission Electron Microscopy (TEM) [11][12][13]. These techniques allow a visualization of the nanoscale glass structure, especially as extended phase separation occurs [14].…”