Shirai Koun, Watanabe Kota, Momida Hiroyoshi, Hyun Sangil
SANKEN, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan.
Vietnam Japan University, Vietnam National University, Hanoi, Luu Huu Phuoc Road, My Dinh 1 Ward, Nam Tu Liem District, Hanoi, Vietnam.
J Phys Condens Matter. 2023 Sep 15;35(50). doi: 10.1088/1361-648X/acf6ec.
The most important characteristic of glass transition is a jump in the specific heatΔCp. Despite its significance, no standard theory exists to describe it. In this study, first-principles molecular-dynamics simulations are used to describe the glass transition of silica glass. The novel view that state variables are extended to include the equilibrium positions of atoms{R-j}is fully used in analyzing the simulation results. Decomposing the internal energy into three components (structural, phonon, and thermal expansion energies) reveals that the jumpΔCpof silica glass is entirely determined by the component of structural energy. The reason for the smallΔCpis its high glass-transition temperature, which makes the fluctuation in the structural energy insensitive to the temperature change. This significantly affects how the Prigogine-Defay ratiois interpreted, which was previously unknown. The ratiorepresents the ratio of the total energy change to the contribution of thermal expansion energy at the glass transition. The general property,> 1, of glasses indicates that glass transitions occur mainly via the change in the structural energy. Silica glass is an extreme case in that the transition occurs entirely through the change in internal structure, such as the distribution of the bending angle of Si-O-Si bonds.
玻璃化转变最重要的特征是比热ΔCp出现跃升。尽管其意义重大，但尚无描述它的标准理论。在本研究中，采用第一性原理分子动力学模拟来描述石英玻璃的玻璃化转变。在分析模拟结果时充分运用了将状态变量扩展到包括原子{R-j}平衡位置的新观点。将内能分解为三个分量（结构能、声子能和热膨胀能）表明，石英玻璃的比热跃升ΔCp完全由结构能分量决定。ΔCp较小的原因是其玻璃化转变温度较高，这使得结构能的波动对温度变化不敏感。这对普利高津-德法依比的解释产生了重大影响，而这在以前是未知的。该比值表示玻璃化转变时总能量变化与热膨胀能贡献的比值。玻璃的一般性质γ>1表明玻璃化转变主要通过结构能的变化发生。石英玻璃是一个极端例子，其转变完全通过内部结构的变化发生，例如Si-O-Si键弯曲角的分布。
