  In network glass including chalcogenides, the network topology of microscopic
structures can be tuned by changing the chemical compositions. As the
composition is varied, an intermediate phase (IP) singularly different from the
adjacent floppy or rigid phases on sides has been revealed in the vicinity of
the rigidity onset of the network. Glass formers in the IP appear to be
reversible at glass transition and strong in dynamical fragility. Meanwhile,
the calorimetry experiments indicate the existence of a first-order
liquid-liquid transition (LLT) at a temperature above the glass transition in
some strong glass-forming liquids. How are the intermediate phase and the
liquid-liquid transition related? Recent molecular dynamics simulations hint
that the intermediate phase is thermodynamically distinct that the transitions
to IP as varying the chemical composition in fact reflect the LLT: out of IP,
the glass is frozen in vibrational entropy-dominated heterogeneous structures
with voids; while inside IP, energy dominates and the microscopic structures of
liquids become homogeneous. Here we demonstrate such first-order thermodynamic
liquid-liquid transition numerically and analytically in an elastic network
model of network glass and discuss possible experimental approaches to testify
the connection.
