Voronoi Structural Evolution of Bulk Silicon upon Melting

Abstract

The Voronoi structural evolution of silicon upon melting is investigated using a molecular dynamics simulation. At temperatures below the melting point, the solid state system is identified to have a four-fold coordination structure ⟨4, 0, 0, 0⟩. As the temperature increases, the five-fold coordination ⟨2, 3, 0, 0⟩ and six-fold coordination structures ⟨2, 2, 2, 0⟩ and ⟨0, 6, 0, 0⟩ are observed. This is explained in terms of increasing atomic displacement due to thermal motion and the trapping of the moving atoms by others. At temperatures above the melting point, nearly all of the four-fold coordination structures grows into multiple-fold coordination ones.

Polymorphism in glassy silicon: Inherited from liquid-liquid phase transition in supercooled liquid

“…The Voronoi polyhedron method has been proven to be effective for the analyses of local atomic environment 31 and the volume of cluster 32 in liquids and glasses. The Voronoi index is expressed as < n 1 ,n 2 ,n 3 ,n 4 >, where n i denotes the number of i -edged faces of the Voronoi polyhedrons 33 34 35 . Figure 5 shows the voronoi structure obtained from four typical cooling rates (a) cr1 = 5 × 10 10 K/s, (b) Cr3 = 5 × 10 11 K/s, (c) Cr6 = 1 × 10 13 K/s and (d) Cr8 = 1 × 10 14 K/s.…”

“…In our previous wrok 33 , it was shown that the <4, 0, 0, 0> is the diamond crystal structure and existed in the crystal silicon. This structure makes the crystal silicon show semiconducting behaviors.…”

“…The <2,3,0,0> is the main component in the LDL. The <4,0,0,0> can be transformed from the <2,3,0,0> as an atom is released 33 . The <4,0,0,0>-based glass is composed mainly of the four-fold structure <4, 0, 0, 0> and the less five-fold structure <2, 3, 0, 0>.…”

“…The system includes 4096 silicon atoms with periodic boundary condition (PBC). The atomic interactions are described using the Stillinger–Weber potential (SW potential) 37 , which is known to reproduce qualitatively the behavior of silicon well 33 38 . To obtain the supercooled liquid, the initial equilibrium liquid drop some temperature, such as 10 K, and repeat a relaxation under constant number, pressure, temperature (NPT) ensemble.…”