Phase-Transition Dynamics of Forsterite from Glass to Liquid States

Abstract

To investigate the transition mechanisms of forsterite from a glassy to molten state, we performed molecular dynamics calculations in a temperature range of 10–3000 K. The results show that the thermal expansion coefficient changes remarkably at around 1567 K during heating from 10 K. This temperature is the transition point from glassy to liquid states. To investigate the mechanisms of the phase transition, shear viscosity and self-diffusion processes of atoms were analyzed. The result shows that the increasing rates of diffusion coefficients with heating change at around 1300 and 1800 K. This suggests that a diffusion mechanism changes in the supercooled liquid state. From the observation of the trajectories of atoms, it was found that atoms migrate through discontinuous hopping in the supercooled liquid matrices. The hopping probability of atoms, which is located in positions with higher Si and lower Mg densities, is higher than the average probability at low temperatures. The result indicates a dynamical correlation between the hops of atoms in the supercooled liquid state, while Brownian motion is the main mechanism of diffusion in the liquid phase at temperatures above the melting point. The mechanism of the glass–liquid transition of forsterite is important for understanding the evolution process of minerals in space.

Structures and Dynamics of Forsterite and Its Interstitial Water

“…The potential parameters used in the present study were listed in our previous paper . The values were empirically determined by constraining the model to reproduce the experimental results of the density, thermal expansion coefficient, and bulk modulus for forsterite and ice in the crystal and amorphous states. − …”