Heat capacity and the orientational transition in solid C60.
Heat capacity and the orientational transition in solid C60.
复制标题
固体 C60 中的热容和取向转变。
DOI：
10.1103/physrevb.53.11418
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发表时间：
1996
期刊：
影响因子：
--
通讯作者：
ter Meer H
中科院分区：
文献类型：
--
作者：
Fischer;McGhie;Estrada;Haluska;Kuzmany;ter Meer H
我们报告的近绝热热容数据的高纯度粉末和单晶C 60，通过调制差示扫描量热法，便于数据收集上一个非常精细的温度网格。与取向熔化转变相关的反常在260 K比以前报道的更尖锐和更明显，最好的样品的半峰全宽≤ 0.2 K。来自三个不同来源的粉末和晶体样品都显示出0.1-0.3 K的异常分裂，冷却比加热更明显。在几种可能的解释中，最吸引人的（最近的扩散X射线和中子散射结果的动机）是发生的中间有序相的对称性不同的Pa 3基态。在粉末样品中，熔化和冻结起始之间的滞后≤ 0.1 K，但在晶体中≥ 1 K，我们将其归因于晶体中的成核限制冻结。我们没有发现最近报道的一些效应的证据，包括165 K和290 K之间的滞后行为以及240 K和300 K附近的额外转变。
We report near-adiabatic heat capacity data on high-purity powder and single crystal C 60, obtained by modulated differential scanning calorimetry which facilitates data collection on a very fine temperature mesh. The anomaly associated with the orientational melting transition at∼ 260 K is much sharper and more pronounced than previously reported, the full width at half maximum in the best sample being≤ 0.2 K. Powder and crystal samples from three different sources all show a 0.1–0.3 K splitting of the anomaly, more pronounced on cooling than on heating. Among several possible interpretations, the most appealing (motivated by recent diffuse x-ray and neutron scattering results) is the occurrence of an intermediate ordered phase with symmetry different from that of the Pa3 ground state. Hysteresis between melting and freezing onsets is≤ 0.1 K in powder samples but≥ 1 K in crystals, which we attribute to nucleation-limited freezing in the latter. We find no evidence for a number of effects reported recently, including hysteretic behavior between 165 K and 290 K and additional transitions near 240 K and 300 K.© 1996 The American Physical Society.