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

TL;DR

This study uses molecular dynamics simulations to explore how binary mixtures transition among crystal, glass, and liquid states by varying particle size ratios and temperature, focusing on defect structures and disorder measures.

Contribution

It introduces a visual and quantitative analysis of defect structures and disorder parameters during phase transitions in binary mixtures.

Findings

Defect proliferation characterizes phase transitions.

Disorder parameter D(t) effectively measures overall disorder.

Relaxation of D(t) slows at low temperatures with size dispersity.

Abstract

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 "D_j(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 "D_j(t)" over the particles, we define a disorder parameter "D(t)", which conveniently measures the degree of overall disorder. Its relaxation 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.