Structural Similarity on Multiple Length Scales and Its Relation to Devitrification Mechanism: A Solid-State NMR Study of Alkali Diborate Glasses and Crystals

Abstract

The nature of the devitrification process is a fundamental problem in glass science and governs the ultimate stability of glass. It is hypothesized that the devitrification mechanism of a given glass composition is strongly correlated with the extent of structural similarity at the intermediate-range level between the glass and crystal phase to which it transforms. However, relatively little information is available to test this hypothesis because of the lack of long-range periodicity in glass and the absence of effective analysis methods. In this work Li 2 O-2B 2 O 3 (L2B) and Na 2 O-2B 2 O 3 (N2B) glasses, which respectively exhibit homogeneous (internal) and heterogeneous (surface) devitrification mechanisms, and corresponding crystals were prepared and comprehensively studied by using multiple solid state NMR techniques. Of those, 11B MAS and MQMAS experiments were applied to reveal short-range order information; Na} rotational echo double resonance (REDOR) experiments were used to determine homonuclear and heteronuclear interactions that can reflect the intermediate-range order. It was found that the local bonding environments of the L2B crystal and glass are quite similar, whereas there are significant differences in the N2B system. Moreover, the experimental results indicated that the second moment (M 2 ) values of both homo-and heterodipolar interactions measured for the L2B glass are very close to those of its isochemical crystal, in contrast, the M 2 values for N2B glass differ significantly from those of its crystal phase. These observations indicate the existence of a strong correlation between structural similarity at both the short and intermediate length scale, and nucleation mechanism.

Spectroscopic Investigation and Crystallization Study of Rare Earth Metaborate Glasses

“…These direct observations are in accordance with DTA measurements performed on samples with increasing grain sizes, which will be presented elsewhere, showing that the crystallization is highly heterogeneous. This observation suggests that the structure of the glass is different from the one of the crystal, in accordance with spectroscopic results above and similarly as other studies performed on alkali borate glasses (Chen et al (2009(Chen et al ( ), (2010). g c Figure 3.…”

Spying with spins on messy materials: 60 Years of glass structure elucidation byNMRspectroscopy

“…For such glass systems, various macroscopic properties, such as densities, configurational entropies, and frozen‐in birefringence, have suggested that the structure in the glassy state shows a closer resemblance to the structure of the phase formed upon crystallization than in the case of glass systems only undergoing heterogeneous nucleation. This result has been supported by solid‐state NMR techniques on some important benchmark alkali silicate and borate glasses . This work suggested in particular that dipolar second moments quantifying network modifier‐network modifier and network modifier‐network former interactions might form a particularly useful measure for probing structural resemblance or distinction between crystalline and glassy phases in the context of homogeneous nucleation ability.…”

“…This work suggested in particular that dipolar second moments quantifying network modifier‐network modifier and network modifier‐network former interactions might form a particularly useful measure for probing structural resemblance or distinction between crystalline and glassy phases in the context of homogeneous nucleation ability. For example, 11 B{ 6 Li} and 11 B{ 23 Na} rotational‐echo double‐resonance (REDOR) experiments indicate much smaller ΔM 2 / M 2c values for lithium diborate (homogeneous nucleation) than for sodium diborate (heterogeneous nucleation) . This hypothesis was subsequently tested by a review of all the relevant data presently in the literature on homogeneously and heterogeneously crystallizing stoichiometric glass systems .…”

Nucleation in Glasses – New Experimental Findings and Recent Theories

“…In this case, similarities in the local or medium range order are important to understand homogeneous nucleation (Chen et al, 2010;Chen, 2009;Longstaffe et al, 2008;Muller et al, 1993;Schneider et al, 2000), since small local atomic reorganization can be involved. Incongruent crystallization implies a more complex mechanism due to the transport of matter over large distances.…”