Low-temperature specific heat and thermal conductivity of a glassy polymer under applied pressure.
Low-temperature specific heat and thermal conductivity of a glassy polymer under applied pressure.
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DOI：
10.1103/physrevb.40.1901
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发表时间：
1989-07
影响因子：
3.7
通讯作者：
Grace Jm;Anderson Ac
中科院分区：
文献类型：
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作者：
Grace Jm;Anderson Ac
非晶态聚合物的低温热性质被用来探测玻璃化行为作为压力的函数。具体地，在0.3-10 K的范围内，在高达约4 kbar的压力下测量环氧树脂的热扩散率scra和热导率κ。从κ/scra确定的比热被观察到随压力而降低;在整个温度范围内，相对变化相当均匀。热导率的测量结果表明，温度高于1 K时，电导率随压力的增加而增加。在较低的温度下，这种压力诱导的κ增加的幅度较小;在0.3 K附近，测量结果表明κ随着压力的施加而降低。使用隧道模型对这些测量结果进行分析表明，两能级激发的能量密度随着压力的增加而降低，而这些激发与声子的耦合增加。在0.3-1-K范围内测量到的变化表明，二能级系统的密度取决于声子速度v，即v− 3。在1-10 K范围内的压力引起的变化的幅度表明，在这个制度中的强声子散射和过度激发是最有可能不相关的玻璃中的结构长度尺度。最后，在整个温度范围内，压力的类似变化表明，所有的激发，即声子，二能级系统，和额外的模式高于1 K，是相关的。这些结果进行了讨论方面的隧道模型，微观模型，和分形理论。
The low-temperature thermal properties of an amorphous polymer were used to probe glassy behavior as a function of pressure. Specifically, the thermal diffusivity scra and thermal conductivity κ of an epoxy were measured over the range 0.3–10 K at pressures up to roughly 4 kbar. The specific heat determined from κ/scra was observed to decrease with pressure; the relative changes were rather uniform over the entire temperature range. The thermal-conductivity measurements revealed an increased conductivity with pressure for temperatures above 1 K. The magnitude of this pressure-induced increase in κ was smaller at lower temperatures; near 0.3 K, the measurements indicated decreased κ as pressure was applied. Analysis of these measurements using the tunneling model suggests that the energy density of two-level excitations decreases with pressure, while the coupling of these excitations to phonons increases. The measured changes in the 0.3–1-K regime indicate that the density of two-level systems depends on the phonon velocity v as v− 3. The magnitude of the pressure-induced changes in the range 1–10 K suggests that the strong phonon scattering and excess excitations in this regime are most likely not related to structural length scales in the glass. Finally, the similar changes with pressure over the entire temperature range suggest that all the excitations, namely phonons, two-level systems, and the additional modes above 1 K, are related. These results are discussed with regard to the tunneling model, microscopic models, and the fracton theory.