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Séminaire MCBT

Mardi 30 janvier à 11h00,
Salle Louis Weil, E424

Orateur : Giancarlo JUG (DiSAT - Università dell’Insubria)
"The Intermediate-range Atomic Structure of Glasses as revealed by their Permanent Coherently-tunneling Currents"

ABSTRACT

The intermediate-range atomic structure of melt-quenched glasses and other amorphous solids such as semiconducting thin films is still believed to be described by the Continuous Random Network (CRN) model, or the Bernal model for metallic glasses. However, there is mounting theoretical and experimental evidence that the real structure is in fact cellular-like with small, nm-scale regions of close-packed, better-ordered, solid-like matter and liquid-like matter of similar composition filling the voids (or "cages") between the cells. This structure corresponds to the ideas of "crystallites" or "paracrystals" occasionally found in glass and amorphous films literature and - for bulk glasses - it is the direct thermal-history continuation below Tg of the dynamical heterogeneities of the super-cooled liquid state. It will be reviewed how the above cellular structure is the natural explanation for a range of puzzling experiments carried out on non-metallic glasses and amorphous films at low temperatures, with and without an applied magnetic field. Then, new magnetization data will be discussed for some non-magnetic multi-silicate glasses where the presence of iron-impurities is not sufficient to account for the observed temperature and magnetic-field dependence. These experiments are the ultimate proof for the presence in all glasses of coherently-tunneling permanent mesoscopic currents residing within the liquid-like "cages". By exploiting the measurements at the lower temperatures, the size of the solid-like cells can be estimated and compared to existing electron-microscopy imaging. An important consequence of these observations and of their theory is the demise of the CRN scenario and a completely new kinetic approach to the glass-formation mechanism. Moreover, recent XPCS synchrotron-radiation measurements on non-metallic glasses near Tg begin in this way to find their rational explanation.

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