Science and Technology Division, Corning Incorporated, SP-FR-05-1, Corning, New York 14831, USA.
J Chem Phys. 2010 Oct 28;133(16):164503. doi: 10.1063/1.3499326.
A common assumption in the glass science community is that the entropy of a glass can be calculated by integration of measured heat capacity curves through the glass transition. Such integration assumes that glass is an equilibrium material and that the glass transition is a reversible process. However, as a nonequilibrium and nonergodic material, the equations from equilibrium thermodynamics are not directly applicable to the glassy state. Here we investigate the connection between heat capacity and configurational entropy in broken ergodic systems such as glass. We show that it is not possible, in general, to calculate the entropy of a glass from heat capacity curves alone, since additional information must be known related to the details of microscopic fluctuations. Our analysis demonstrates that a time-average formalism is essential to account correctly for the experimentally observed dependence of thermodynamic properties on observation time, e.g., in specific heat spectroscopy. This result serves as experimental and theoretical proof for the nonexistence of residual glass entropy at absolute zero temperature. Example measurements are shown for Corning code 7059 glass.
玻璃科学领域的一个常见假设是，通过对玻璃转变过程中测量的热容曲线进行积分，可以计算出玻璃的熵。这种积分假设玻璃是一种平衡材料，玻璃转变是一个可逆过程。然而，作为一种非平衡和非遍历材料，平衡热力学的方程不能直接应用于玻璃态。在这里，我们研究了在诸如玻璃等非遍历系统中热容和构型熵之间的关系。我们表明，一般来说，不可能仅从热容曲线计算玻璃的熵，因为必须知道与微观涨落细节有关的其他信息。我们的分析表明，时间平均形式对于正确解释实验观察到的热力学性质对观察时间的依赖性（例如在比热光谱学中）是必不可少的。这一结果为在绝对零度下不存在残余玻璃熵提供了实验和理论上的证明。以康宁代码 7059 玻璃为例进行了测量。
