Elemental and cooperative diffusion in a liquid, supercooled liquid and glass resolved

Abstract

The diffusion mechanisms controlling viscous flow, structural relaxation, liquid-liquid phase separation, crystal nucleation, and crystal growth in multicomponent glass-forming liquids are of great interest and relevance in physics, chemistry, materials, and glass science. However, the diffusing entities that control each of these important dynamic processes are still unknown. The main objective of this work is to shed some light on this mystery, advancing the knowledge on this phenomenon. For that matter, we measured the crystal growth rates, the viscosity, and lead diffusivities in PbSiO liquid and glass in a wide temperature range. We compared our measured values with published data covering 16 orders of magnitude. We suggest that above a certain temperature range T (1.2T-1.3T), crystal growth and viscous flow are controlled by the diffusion of silicon and lead. Below this temperature, crystal growth and viscous flow are more sluggish than the diffusion of silicon and lead. Therefore, T marks the temperature where decoupling between the (measured) cationic diffusivity and the effective diffusivities calculated from viscosity and crystal growth rates occurs. We reasonably propose that the nature or size of the diffusional entities controlling viscous flow and crystal growth below T is quite different; the slowest is the one controlling viscous flow, but both processes require cooperative movements of some larger structural units rather than jumps of only one or a few isolated atoms.

Viscosity and liquidus‐based predictor of glass‐forming ability of oxide glasses

“…Regarding the 2D growth model, besides the influence of the jump distance, the calculated crystal growth rates can vary considerably between glass‐forming melts due to the strong dependence on the crystal‐melt interfacial energy. Within the glass‐forming systems used in this work, literature results and our own analysis (not shown here) suggest that the growth rates of SB 2 , BB 2 , BB 4 , LB 2 , PS 2, PS, and B 2 TS 2 could also fit the 2D model . Figure shows that the data referring to these glasses are also scattered over a relatively wide region.…”

“…Within the glass-forming systems used in this work, literature results and our own analysis (not shown here) suggest that the growth rates of SB 2 , BB 2 , BB 4 , LB 2 , PS 2, PS, and B 2 TS 2 could also fit the 2D model. 50,52,62,65,72 Figure 5 shows that the data referring to these glasses are also scattered over a relatively wide region. It is impossible, therefore, to assign a distinct region for SD and 2D models.…”

“…Several works 44,48 successfully connected D U with the shear viscosity of the supercooled liquid using the Stokes-Einstein-Eyring equation, 49 but this connection breaks down for temperatures below 1.1-1.2T g . 44,[50][51][52] Fortunately, however, this break is not relevant for this particular work because we will be dealing with crystallization at much higher temperatures, near to the nose of the TTT curves, which are close to T L . Equation 2 shows that on a TTT curve, the time needed to reach a certain surface crystallized fraction at each temperature is given by…”

Solving the classical nucleation theory with respect to the surface energy

“…This solution may also be used, for example, when dealing with crystal growth mediated by secondary surface nucleation (see Ref. [14]). The fact that a solution is possible does not imply that it is non-complex.…”

The diffusion coefficient controlling crystal growth in a silicate glass‐former

“…However, one faces some adversities when studying the physics of crystal growth. One of the most relevant is our ignorance of what the diffusing entities (or structural entities ) are that control this phenomenon . The glass research community does not know if crystal growth kinetics is controlled by 1 chemical element (e.g.…”