51 V and 133 Cs MAS NMR Investigation of Crystalline Trivanadate and Hexavanadate Phases
- PDF / 315,579 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 103 Downloads / 186 Views
0984-MM07-03
V and 133Cs MAS NMR Investigation of Crystalline Trivanadate and Hexavanadate Phases.
Olivier Durupthy, Jocelyne Maquet, Nathalie Steunou, Christian Bonhomme, and Jacques Livage University Paris 6, Chimie de la Matière condensée de Paris UMR 7574, 4 place jussieu, Paris cedex 05, 75252, France
ABSTRACT A complete solid state NMR characterization of the vanadium oxides Cs[V3O8] and Cs2[V6O16].0.7H2O is proposed. We used 51V and 133Cs MAS NMR to investigate the local environment of cesium and vanadium nuclei and 2D 1H-133Cs CP MAS HETCOR experiments to explore the connectivities between cesium ions and water molecules in the interlamellar space. INTRODUCTION M[V3O8] (M=Li, Na, Cs, …) compounds are promising candidates as reversible cathodes in lithium batteries [1]. Depending on the synthesis route, the trivanadate phases exhibit different structural features (size, shape and organization of particles) that influence directly their electronic properties. For instance, the low-temperature form of Lix[V3O8] is able to accommodate 4.5 mol of Li+ ions per formula unit, instead of 3 for the high temperature trivanadate [2]. An accurate characterization of these phases is therefore quite interesting in order to predict or to explain their electronic properties. Since some of these vanadate phases exhibit a significant crystallographic disorder, solid state NMR may be a complementary tool of characterization to X-ray diffraction. Here, we report a detailed solid state NMR characterization of Cs[V3O8] and Cs2[V6O16].0.7H2O phases, that were prepared by a sol-gel synthesis approach. These compounds were studied by 51V and 133Cs MAS NMR spectroscopy in order to investigate the local environment of vanadium and cesium cations, respectively. In addition, the interlamellar space was also studied by 2D 1H-133Cs CP MAS HETCOR (HETeronuclear CORrelation) experiments. Such 1H-133Cs CP MAS NMR correlation studies, that have never been reported so far, allow the identification of at least four different cesium sites in the Cs2[V6O16].0.7H2O structure based on their proximity with water protons.
THEORY (OR EXPERIMENT) Cs[V3O8] and Cs2[V6O16].0.7H2O have been prepared according to a procedure previously used for the synthesis of Na0.3V2O5.1.5H2O and NaV3O8.1.5H2O [3]. This synthesis route is based on the addition of CsOH and CsCl solutions (2 mol.L-1) to an acidified metavanadate (NaVO3) solution in order to set the initial pH to defined initial values varying from 1 to 4. A yellow precipitate (YP) and a yellow-orange precipitate (YOP) were isolated. The X-ray diffraction pattern of YP is identical to the one reported for Cs[V3O8] compound [4]. Moreover, the chemical analyses show that the Cs/V ratio is close to 0.33, in agreement with the Cs[V3O8] chemical composition. The X-ray diffraction pattern of YOP is in fair agreement with
the reported pattern of the hexavanadate phase Cs2[V6O16].1.5 H2O (JCPDS 51-0378) [5]. The thermogravimetric analysis of YOP shows that the water content is presumably close to 0.7 per formul
Data Loading...
