Fragile-to-strong transition in liquid silica

Abstract

We investigate anomalies in liquid silica with molecular dynamics simulations and present evidence for a fragile-to-strong transition at around 3100 K-3300 K. To this purpose, we studied the structure and dynamical properties of silica over a wide temperature range, finding four indicators of a fragile-to-strong transition. First, there is a density minimum at around 3000 K and a density maximum at 4700 K. The turning point is at 3400 K. Second, the local structure characterized by the tetrahedral order parameter changes dramatically around 3000 K from a higher-ordered, lower-density phase to a less ordered, higher-density phase. Third, the correlation time τ changes from an Arrhenius behavior below 3300 K to a Vogel-Fulcher-Tammann behavior at higher temperatures. Fourth, the Stokes-Einstein relation holds for temperatures below 3000 K, but is replaced by a fractional relation above this temperature. Furthermore, our data indicate that dynamics become again simple above 5000 K, with Arrhenius behavior and a classical Stokes-Einstein relation.

The structural transition under densification and the relationship between structure and density of silica glass

“…Liquid-liquid phase transition, which results in the regions with different densities in liquid system as temperature or pressure are varied. Namely, the phase transition from low density (LD) to high-density (HD) form has also been shown by experiments and molecular dynamics simulation [5,[34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] for H 2 O, Si, SiO 2 , Al 2 O 3 -Y 2 O 3 , . .…”

“…So, silica as well as silicate glasses are interesting to scientists in the areas of physics and materials science. Investigating the structure of silica glass is expected to clarify the physical properties and behavior of Si-O network structure [1][2][3][4][5][6][7] under the changes of pressure and temperature. At low pressure, the relatively-rigid SiO 4 tetrahedron is the basic structural unit in silica/silicate glasses and melts: each Si connects to four nearest neighbor O atoms, with Si-O bond length of approximately 1.62 Å, and each O links to two nearest neighbor Si atoms [8][9][10][11].…”

“…MD simulation using the semiempirical interatomic potentials [9][10][11][17][18][19][20] reproduces well the samples of silica and silicate glasses/melts with the characteristics in good agreement with experimental data. Simulations in works [5,21,22] reveals that the silica/silicates show several anomalies including: density anomaly, diffusion anomaly, spinodal instability and structural phase transition. As the silica/silicates are densified, the system gradually transforms from tetrahedral-to octahedral-network structure.…”

“…It has been shown that, Silica has four major polymorphs: Cristobalite, Tridymite, Quartz and glass. A lot of theoretical calculations, computer simulation and experimental measures concerning with the behavior of various high-pressure silica phases (keatite, coesite, stishovite, CaCl 2 -, a-PbO 2 -, I2/a, baddeleyite, fluorite, and pyrite(Pa-3)-types) [4][5][6] have been carried out for many decades. Total energy calculations using ab initio method for specific structures have provided an explanation for structural transformation from amorphous to crystalline silica [30].…”

Properties of Hydrogen-Bonded Liquids at Interfaces

“…Moreover, they argued that such LL transition can cause a FS transition. The predictions of this model were further explored in molecular dynamics (MD) simulations on water-like [111] and silica-like [112] bulk liquids, where the partial charges of the atoms were purposely scaled to systematically vary the Coulomb interactions.…”