Insertion of Oxide Clusters and Poly (Phenylene Vinylene) in MoO 3 by Ion Exchange
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INSERTION OF OXIDE CLUSTERS AND POLY (PHENYLENE VINYLENE) IN MoO 3 BY ION EXCHANGE *L.F. NAZAR, X.T. YIN, D. ZINKWEG, Z. ZHANG, and S. LIBLONG Guelph-Waterloo Centre for Graduate Work in Chemistry, University of Waterloo, Department of Chemistry, Waterloo, Ontario, N2L 3G1
ABSTRACT AxMoO (H2 0)y has been shown to undergo substantial exfoliation of the layer structure in water wheen A - Li. Although extensive exfoliation of the Na form is not observed, sufficient swelling occurs to enable the insertion of large polyoxycations of Al, Ga, Zr, Ti and Cr between the layers of MoOn by ion exchange with colloidal dispersions of NaXMoO 3. This represents the first such pillaring" reactions for MoO3 . Interlayer expansions are observed to range from 7 to 14A in these materials. In some cases, the orientation of the oxide cluster between the layers can also be determined by 1D electron density mapping. We have also shown that this method can be applied to the insertion of conductive polymers via incorporation of a water-soluble precursor polymer. The sulfonium ionomer precursor of poly (p-phenylene vinylene) has been intercalated in MoO 3 , to form a novel polymer/oxide layered structure. Data for the heat-treated [PPV] 32 MoO 3 films show an order of magnitude increase in conductivity over that of pristine Naxlb()o3, INTRODUCTION. MoO 3 is a promising material for many solid state ionic applications, including electrochromic devices, and secondary batteries. The most thermodynamically stable phase, cc-MoO 3 , is a layered structure consisting of edge and vertex bonded MoO 6 octahedra which form corregated sheets. Studies of Li insertion in this phase, together with other considera tps have led to the conclusion that it is one of the more viable battery cathode materials,l, . However, practical limitations to its use stem from the irreversible structural and morphological changes of the lattice which ocur on cyf ling. This is compounded by relatively Li ion mobility in the structure (D = 1cm- s- ), and the very low electronic conductivity of LixMoO 3 at x=O. Possibilities for overcoming these limitations include either modifying the layer structure to create a three dimensional network, or by perturbing the ionic network to facilitate ion mobility. The search for new polytypes of MoO has recently led to the discovery of a tetragonal phase (B-MoO 3 ) having the ReO 3 structure , and "hexagonal" MoO .4 However, neither of these offer sign-ficant improvements over the layered polytype. Our approach based on the arguments above is twofold. One method we are using is to incorporate large oxide clusters between the layers which can be transformed to oxide pillars by calcination, thus pinning the layers together to form a 3D structure. This method was pioneered in clay research, but has not been successfully extended to many transition metal oxides. Secondly, we are examining the insertion of conductive polymer chains in the interlayer gap. The concept of inclusion of conductive polymer chains5 in layered materials was first demon
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