Scopigno Tullio, Ruocco Giancarlo, Sette Francesco, Monaco Giulio
Istituto Nazionale per la Fisica della Materia and Dipartimento di Fisica, Universitá di Roma La Sapienza, 00185 Roma, Italy.
Science. 2003 Oct 31;302(5646):849-52. doi: 10.1126/science.1089446.
When a liquid is cooled below its melting temperature, it usually crystallizes. However, if the quenching rate is fast enough, the system may remain in a disordered state, progressively losing its fluidity upon further cooling. When the time needed for the rearrangement of the local atomic structure reaches approximately 100 seconds, the system becomes "solid" for any practical purpose, and this defines the glass transition temperature Tg. Approaching this transition from the liquid side, different systems show qualitatively different temperature dependencies of the viscosity, and accordingly they have been classified by introducing the concept of "fragility." We report experimental observations that relate the microscopic properties of the glassy phase to the fragility. We find that the vibrational properties of the glass well below Tg are correlated with the fragility value. Consequently, we extend the fragility concept to the glassy state and indicate how to determine the fragility uniquely from glass properties well below Tg.
当一种液体被冷却到其熔点以下时，它通常会结晶。然而，如果淬火速率足够快，系统可能会保持无序状态，在进一步冷却时逐渐失去流动性。当局部原子结构重排所需的时间达到大约100秒时，从任何实际用途来看，系统都变成了“固体”，这就定义了玻璃化转变温度Tg。从液体一侧接近这个转变时，不同的系统表现出在粘度上定性不同的温度依赖性，因此通过引入“脆性”概念对它们进行了分类。我们报告了将玻璃相的微观性质与脆性联系起来的实验观察结果。我们发现，远低于Tg的玻璃的振动性质与脆性值相关。因此，我们将脆性概念扩展到玻璃态，并指出如何从远低于Tg的玻璃性质唯一地确定脆性。
