Vdovichenko G A, Krivchikov A I, Korolyuk O A, Tamarit J Ll, Pardo L C, Rovira-Esteva M, Bermejo F J, Hassaine M, Ramos M A
B. Verkin Institute for Low Temperature Physics and Engineering of NAS Ukraine, 47 Lenin Ave., 61103 Kharkov, Ukraine.
Grup de Caracterització de Materials, Departament de Física i Enginyeria Nuclear, ETSEIB, Universitat Politècnica de Catalunya, Diagonal 647, 08028 Barcelona, Catalonia, Spain.
J Chem Phys. 2015 Aug 28;143(8):084510. doi: 10.1063/1.4929530.
The thermal conductivity, specific heat, and specific volume of the orientational glass former 1,1,2-trichloro-1,2,2-trifluoroethane (CCl2F-CClF2, F-113) have been measured under equilibrium pressure within the low-temperature range, showing thermodynamic anomalies at ca. 120, 72, and 20 K. The results are discussed together with those pertaining to the structurally related 1,1,2,2-tetrachloro-1,2-difluoroethane (CCl2F-CCl2F, F-112), which also shows anomalies at 130, 90, and 60 K. The rich phase behavior of these compounds can be accounted for by the interplay between several of their degrees of freedom. The arrest of the degrees of freedom corresponding to the internal molecular rotation, responsible for the existence of two energetically distinct isomers, and the overall molecular orientation, source of the characteristic orientational disorder of plastic phases, can explain the anomalies at higher and intermediate temperatures, respectively. The soft-potential model has been used as the framework to describe the thermal properties at low temperatures. We show that the low-temperature anomaly of the compounds corresponds to a secondary relaxation, which can be associated with the appearance of Umklapp processes, i.e., anharmonic phonon-phonon scattering, that dominate thermal transport in that temperature range.
在低温范围内，已在平衡压力下测量了取向玻璃形成剂1,1,2-三氯-1,2,2-三氟乙烷（CCl₂F - CClF₂，F - 113）的热导率、比热容和比容，结果显示在约120、72和20 K处存在热力学异常。将这些结果与结构相关的1,1,2,2-四氯-1,2-二氟乙烷（CCl₂F - CCl₂F，F - 112）的结果一起讨论，F - 112在130、90和60 K处也显示出异常。这些化合物丰富的相行为可以通过它们几个自由度之间的相互作用来解释。对应于内部分子旋转的自由度的冻结，导致了两种能量上不同的异构体的存在，以及作为塑性相特征取向无序来源的整体分子取向，分别可以解释较高温度和中间温度下的异常。软势模型已被用作描述低温下热性质的框架。我们表明，这些化合物的低温异常对应于二次弛豫，这可能与Umklapp过程的出现有关，即非谐声子 - 声子散射，它在该温度范围内主导热传输。
