On the structural heterogeneity of supercooled liquids and glasses ^(a)

Abstract

The status of our basic understanding of the physics and structure of glasses is presented in the light of recent developments in the experimental, phenomenological, and numerical approach to the description of real systems. Spontaneous and induced dynamic heterogeneities appear in the supercooled state of liquids and become frozen intact below the glass transition point. In most cases, mesoscopic heterogeneities due to partial microphase separation are frozen in glasses. Thus, glasses can be described as dynamically arrested heterogeneous supercooled liquids with more solid-like and liquid-like nanoscale regions. The critical issue is that, depending on material type and temperature, the heterogeneities exhibit different size distributions with the solid-like regions probably displaying a degree of hidden quasi-order. This scenario naturally explains some of the important physical properties of real glasses.

Point-defect avalanches mediate grain boundary diffusion

“…Although such measurements do not give detailed information about specific mechanisms and are limited to elements with available isotopes, their application to GB diffusion could still be attempted to confirm the existence of collective atomic rearrangements predicted by the simulations. Dielectric spectroscopy methods have also been used in specific glasses and supercooled liquids to resolve the characteristic frequencies of slow and fast processes during glassy dynamics [40][41][42] . They, too, could potentially be used to gain at least some insights into the GB diffusion dynamics on the atomic level.…”

Revealing the Intrinsic Magnetism of Non-Magnetic Glasses

“…7(a) we show a HRTEM (high-resolution transmission electron-microscopy) image [40] of the structure of a typical silicate glass, where the random closed-packed arrangement of these RER is apparent. Vogel [41] has produced many of such HRTEM pictures for network glasses, showing that the structure here advocated for is generic for any glass [15,11,12]. There is in fact reasonably good agreement between the size 2ξ of the RER as estimated in HRTEM and what is deduced from the concentration of the coherent-tunneling quasiparticles obtained by theory-fitting a wide spectrum of experiments on glasses in magnetic fields at Kelvin and sub-Kelvin temperatures [11].…”

“…Here, the "amorphous" solid state is made up of solid-like particle regions -jammed together below T gand liquid-like particle regions in between [11]. The solid-like regions are also known to be better-ordered as well [12,35,36], at least there is strong evidence just above T g [37,38], hence they are called RER (regions of enhanced regularity) in the glass. The particles that are more mobile -also those proximal to RER walls, which are most likely charged O − dangling bonds for the multi-silicate glasses -get to be squeezed together in the "voids" between the solid-like RER which themselves make up a close-packed true random solid.…”

“…However, other scientists have suggested to further elaborate upon the CRN approach in favour of heterogeneous mesoscopic scenarios [1,2,5,6,7,10]. Moreover, scenarios have been proposed where the dynamical heterogeneities (DH) known to characterise the supercooled liquid state [13] continue to exist (albeit somewhat more statically) also below T g , the nominal temperature of glass formation [8,9,11,12]. One of these non-CRN scenarios views glasses as made up of solid-like particle regions jammed together somewhat below T g and presenting liquid-like regions in-between [11].…”

Medium Range Ordering in liquid Al-based alloys: towards a machine learning approach of solidification

“…Conversely, diffusion is strongly influenced by the local order in the liquid phase. Upon cooling in the metastable undercooled state, the liquid becomes progressively more viscous and the dynamics changes significantly, exhibiting Arrhenius-to-non-Arrhenius crossovers of diffusion, viscosity and structural relaxation time, the occurrence of dynamic heterogeneities (DH) and the breakdown of the Stokes−Einstein (SE) relation [4][5][6]. Understanding 1274 (2023) 012001 IOP Publishing doi:10.1088/1757-899X/1274/1/012001 2 the underlying physics remains a major challenge to characterize order in disorder and to establish structure-dynamics relations from the experimental and simulation point of view.…”