Polyamorphism of liquid silica under compression based on five order-parameters and two-state model: a completed and unified description

ABSTRACT

The polyamorphism of liquid silica (SiO₂) at 3200 K and in a wide pressure range is investigated by molecular dynamics simulation. Results show that the structure of liquid SiO₂ consists of five order-parameters that do not depend on compression. Three order parameters that relate to the short-range order are SiO_x coordination units (x = 4, 5, 6) and two order parameters that relate to the intermediate-range order are OSi₂ and OSi₃ linkages. The structure of liquid silica under compression can be described by the two-state model: low-density and high-density states. The low-density state is formed by clustering of OSi₂ linkages (in the low-density state, the short-range order (SRO) is mainly characterized by SiO₄ coordination units), conversely, clustering of OSi₃ linkages will form high-density state (in the high-density state, the SRO is mainly characterized by SiO₅ and SiO₆ coordination units). Under compression, in the liquid silica co-exist two phases: low-density and high-density phases. The size of phase regions significantly depends on compression.

KEYWORDS:

• Simulation
• molecular dynamics
• network forming liquid

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes on contributors

L. T San received her master degree in Engineering Physics from School of Engineering Physics (SEP), Hanoi University of Science and Technology (HUST). At present, she is studying PhD program at SEP.

N. V. Hong is an Associate Professor at SEP, HUST. He is a lecturer at SEP. He has teaching experience of more than 10 years to students of computational physics and 50 national/international publications in the field of material science.

P. K. Hung is an Associate Professor at SEP, HUST. He is the Head of the Department of Computational Physics. He has teaching experience of more than 20 years to students, masters, PhDs of computational physics and 80 national/international publications in the field of material science.

Additional information

Funding

This research is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number: 103.05–2014.40