Structural origin of negative thermal expansion in high-temperature silica polymorphs

Area of Science:

• Materials Science
• Computational Chemistry
• Solid State Physics

Background:

• Silica polymorphs (quartz, cristobalite) exhibit distinct structural and thermal properties.
• Understanding thermal expansion is crucial for materials applications, especially at high temperatures.

Purpose of the Study:

• To simulate and analyze the thermal expansion behavior of alpha and beta quartz and cristobalite silica.
• To elucidate the atomic mechanisms responsible for negative thermal expansion in silica polymorphs.

Main Methods:

• Molecular dynamics simulations were employed.
• A single charge transfer three-body potential parametrization was utilized for simulations.
• Analysis of atomic trajectories provided insights into atomic motion.

Main Results:

• Simulated alpha silica forms showed positive thermal expansion.
• Beta cristobalite exhibited near-zero thermal expansion up to 1500 K, becoming slightly negative at higher temperatures.
• Beta quartz displayed negative thermal expansion immediately after the alpha-to-beta transition.

Conclusions:

• The study successfully simulated silica polymorphs using molecular dynamics.
• Negative thermal expansion in beta silica forms originates from the reactivation of specific atomic displacement modes.
• These modes are also responsible for the alpha-to-beta phase transformations.