Polymorphic states investigations in thermal conductivity of 1-fluoroadamantane

The temperature dependencies of the thermal conductivity coefficient, κ(T), in 1-fluoroadamantane were investigated for two different orientationally-disordered states. In the first one, κ(T) exhibits a crystalline character with a typical maximum and two anomalous regions marked at higher temperatures. Here, the low-temperature power-law dependence is reduced due to a relatively large contribution of dislocations and defects in the polycrystalline sample. Above 196 K, there is an anomalous plateau in thermal conductivity resulting from the presence of an intermediate centrosymmetric state. Further, a significant increase in κ occurs above 234 K, resulting from a phase transition to a high-temperature disordered cubic phase. Subsequent cooling of the sample leads to an irreversible transition towards a disordered state resulting in a κ(T) dependence corresponding to an amorphous material behavior. The primary anomaly at 196 K disappears, while the second one associated with the phase transition at 227 K shifts towards lower temperatures. The irreversibility of this transformation is also verified by scanning microscopy images. Thermal conductivity in both phases has an additional contribution of an Arrhenius type in their temperature dependences.本研究针对1-氟金刚烷（1-fluoroadamantane）在两种不同取向无序态下的热导率系数κ(T)随温度的依赖关系展开了探究。在第一种取向无序态中，κ(T)表现出晶体特性，呈现典型峰值，并在高温区间出现两处异常区域。此时，由于多晶样品中位错与缺陷的贡献相对较大，低温幂律依赖关系被削弱。当温度高于196 K时，热导率出现异常平台，这源于中间中心对称态的存在。234 K以上热导率显著提升，对应于向高温无序立方相的相变过程。对样品进行后续冷却时，会发生不可逆转变，最终形成无序态，此时κ(T)的温度依赖关系表现出非晶态材料的行为特征。此时，196 K处的主异常峰消失，而与227 K处相变相关的第二处异常峰则向低温方向偏移。该转变的不可逆性也通过扫描显微图像得到了验证。两相中的热导率在其温度依赖关系中均额外包含阿伦尼乌斯型贡献。