Is the Fragility of a Liquid Embedded in the Properties of Its Glass?
Tullio Scopigno,1*
Giancarlo Ruocco,1
Francesco Sette,2
Giulio Monaco2
When a liquid is cooled below its melting temperature, it usually
crystallizes. However, if the quenching rate is fast enough,
the system may remain in a disordered state, progressively losing
its fluidity upon further cooling. When the time needed for
the rearrangement of the local atomic structure reaches approximately
100 seconds, the system becomes "solid" for any practical purpose,
and this defines the glass transition temperature
Tg. Approaching
this transition from the liquid side, different systems show
qualitatively different temperature dependencies of the viscosity,
and accordingly they have been classified by introducing the
concept of "fragility." We report experimental observations that
relate the microscopic properties of the glassy phase to the
fragility. We find that the vibrational properties of the glass
well below
Tg are correlated with the fragility value. Consequently,
we extend the fragility concept to the glassy state and indicate
how to determine the fragility uniquely from glass properties
well below
Tg.
2 European Synchrotron Radiation Facility, BP 220, 38043 Grenoble, France.
* To whom correspondence should be addressed. E-mail: tullio.scopigno{at}phys.uniroma1.it
