Transitions among crystal, glass, and liquid in a binary mixture with changing particle-size ratio and temperature.

Using molecular dynamics simulation we examine changeovers among crystal, glass, and liquid at high density in a two dimensional binary mixture. We change the ratio between the diameters of the two components and the temperature. The transitions from crystal to glass or liquid occur with proliferation of defects. We visualize the defects in terms of a disorder variable Dj(t) representing a deviation from the hexagonal order for particle j. The defect structures are heterogeneous and are particularly extended in polycrystal states. They look similar at the crystal-glass crossover and at the melting. Taking the average of Dj(t) over the particles, we define a disorder parameter D(t), which measures the degree of overall disorder. The relaxation of D(t) after quenching becomes slow at low temperature in the presence of size dispersity. Its steady state average is small in crystal and large in glass and liquid. We also find that grain boundaries tend to be pinned with increasing size dispersity in polycrystal states.