Anion-Promoted Cation Motion and Conduction in Zeolites
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- 作者：Edgar Jordan ; Robert G. Bell ; Dirk Wilmer ; and Hubert Koller
- 刊名：Journal of the American Chemical Society
- 出版年：2006
- 出版时间：January 18, 2006
- 年：2006
- 卷：128
- 期：2
- 页码：558 - 567
- 全文大小：268K
- 年卷期：v.128,no.2(January 18, 2006)
- ISSN：1520-5126
文摘
The motion of sodium cations in sodalite and cancrinite has been investigated by force fieldcalculations, solid-state NMR, and impedance spectroscopy. Special emphasis is dedicated to the influenceof anions on sodium mobilities. Local cation motion is promoted when they interact with anions. However,not all systems with high local mobilities exhibit good ion conductivities, as cooperativity of the motionappears to be an important factor, as well. The activation barrier for local sodium motion (calculations) andlong-range transport (dc conductivities) is lowered in sodalite when halogenide anions, Cl-, Br-, or I-, arepresent. The activation barriers increase with increasing size of the anion and decreasing coordination inthe transition state. On the basis of 23Na solid-state NMR data, all the sodium ions in the dense sodalitestructure are rather rigid up to 470 K. All the cations in chromate sodalite, and Na+ in the small cancrinite
-cages without anion interactions, show a restricted local motion at higher temperatures. There is a selectivehigh local motion of Na+ in the neighborhood of chromate anions in the more open channel system ofcancrinite. These results suggest that sodium migration can be enhanced, at least locally, in open channelsystems by anion interactions. A dynamics coupling between anion reorientation and cation mobility wasnot observed.
-cages without anion interactions, show a restricted local motion at higher temperatures. There is a selectivehigh local motion of Na+ in the neighborhood of chromate anions in the more open channel system ofcancrinite. These results suggest that sodium migration can be enhanced, at least locally, in open channelsystems by anion interactions. A dynamics coupling between anion reorientation and cation mobility wasnot observed.