The Polycluster Theory for the Structure of Glasses: Evidence from Low Temperature Physics

Abstract

The problems of the intermediate-range atomic structure of glasses and of the mechanism for the glass transition are approached from the low-temperature end in terms of a scenario for the atomic organization that justifies the use of an extended tunneling model. The latter is crucial for the explanation of the magnetic and compositional effects discovered in non-metallic glasses in the Kelvin and milli-Kelvin temperature range. The model relies on the existence of multi-welled local potentials for the effective tunneling particles that are a manifestation of a non-homogeneous atomic structure deriving from the established dynamical heterogeneities that characterize the supercooled liquid state. It is shown that the extended tunneling model can successfully explain a range of experiments at low temperatures, but the proposed non-homogeneous atomic structure scenario is then tested in the light of available high resolution electron microscopy imaging of the structure of some glasses and of the behaviour near the glass transition.

Revealing the Intrinsic Magnetism of Non-Magnetic Glasses

“…A better understanding of the atomic nature of the TS is therefore also long awaited for [16]. In this Letter we present what we believe to be an important contribution to furthering knowledge in all of the above-mentioned basic and advanced research areas by providing the first report of the exotic and genuinelymagnetic effect in glasses consistent with the theory briefly outlined above [11,14,15]. A completely new physical effect in glasses, which is weak but laden with important consequences.…”

“…All of these questions and the quest for new technically exploitable or interesting physical effects make glasses a very much active and attractive field of research in condensed matter physics. Where the first of the above questions is concerned -MR structure -several scenarious have been proposed over the last hundred years [1,2,3,4,5,6,7,8,9,10,11]. A much acclaimed approach considers (so-called) network glasses as continuously-and homogeneously-disordered media at the local (atomic), MR and longrange lenght scale: it is the so-called continuous-random-network (CRN) model of Zachariasen and Warren [3,4].…”

“…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].…”

“…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]. Remarkably, the liquid-like regions between the solid ones may become the sources of collective orbital magnetic moments that appear to generate an intrinsic contribution to the glass sample's magnetisation mimicking the known Langevin paramagnetism from isolated impurities.…”

“…In the ordinary silicate glasses the latter are typically from Fe and the Fe-group trace elements [14]. The extra intrinsic magnetic moments issue from specialized, magnetic-field sensitive tunneling systems (TS) believed to be responsible for a plethora of magnetic effects at low temperatures in glasses [11,15,16]. These and the more standard TS (the so-called two-level systems (TLS) [17,18,16]) might be part of the degrees of freedom sought for in order to investigate the physical properties of glasses at higher temperatures too [19].…”