Unusual Relaxation Behavior of Water Inside the Sodalite Cages of Faujasite-Type Molecular Sieves
Unusual Relaxation Behavior of Water Inside the Sodalite Cages of Faujasite-Type Molecular Sieves
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DOI：
10.1021/jp021281v
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发表时间：
2002-08
影响因子：
3.3
通讯作者：
L. Frunza;H. Kosslick;Ş. Frunzǎ;A. Schönhals
中科院分区：
文献类型：
--
作者：
L. Frunza;H. Kosslick;Ş. Frunzǎ;A. Schönhals
用宽带介电谱（10-2 ~ 109 Hz）研究了八面沸石分子筛NaY的分子动力学。直流电导率的贡献和三个弛豫过程中揭示的介电谱。在高频范围内的弛豫过程归因于方钠石笼内的水分子的取向波动进行了详细研究。作为主要结果，我们发现它的平均弛豫时间有一个不寻常的鞍形温度依赖关系，既不服从阿克里乌斯定律，也不服从Vogel-Fulcher-Tammann定律。基于Feldman等人最近开发的模型（J. Phys. Chem. B 2001，105，1845）给出了定量描述，以分析限制在纳米多孔玻璃中的水的动力学。取向波动和缺陷形成的激活能以及缺陷浓度的合理值。
Broad-band dielectric spectroscopy (10-2 to 109 Hz) is applied to investigate the molecular dynamics of NaY, a zeolite of faujasite structure. A dc conductivity contribution and three relaxation processes were revealed in the dielectric spectra. The relaxation process in the high-frequency range ascribed to orientational fluctuations of water molecules inside the sodalite cages is studied in detail. As a main result it is found that its mean relaxation time has an unusual saddle-like temperature dependence, which obeys neither an Arrhenius nor a Vogel−Fulcher−Tammann law. A quantitative description was given on the basis of a model recently developed by Feldman et al. (J. Phys. Chem. B 2001, 105, 1845) to analyze the dynamics of water confined in nanoporous glasses. Reasonable values for the activation energies of orientational fluctuations and of defect formation as well as for the defect concentration were obtained.