Liquid–liquid transition in a strong bulk metallic glass-forming liquid

Abstract

Polymorphic phase transitions are common in crystalline solids. Recent studies suggest that phase transitions may also exist between two liquid forms with different entropy and structure. Such a liquid–liquid transition has been investigated in various substances including water, Al₂O₃-Y₂O₃ and network glass formers. However, the nature of liquid–liquid transition is debated due to experimental difficulties in avoiding crystallization and/or measuring at high temperatures/pressures. Here we report the thermodynamic and structural evidence of a temperature-induced weak first-order liquid–liquid transition in a bulk metallic glass-forming system Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 characterized by non- (or weak) directional bonds. Our experimental results suggest that the local structural changes during the transition induce the drastic viscosity changes without a detectable density anomaly. These changes are correlated with a heat capacity maximum in the liquid. Our findings support the hypothesis that the ‘strong’ kinetics (low fragility) of a liquid may arise from an underlying lambda transition above its glass transition.