Layered V 2 0 5 Xerogels: Host-Guest Chemistry and Conductive-Polymers
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LAYERED V205 XEROGELS:
HOST-GUEST CHEMISTRY AND
CONDUCTIVE-POLYMERS.
Chun-Guey Wu, Mercouri G. Kanatzidis* Department of Chemistry and Center for Fundamental Materials Research, Michigan State University, EastLansing MI 48824 ABSTRACT The properties of vanadium oxide xerogels are reviewed with respect to guest-host chemistry, redox chemistry and electrical charge transport. The insertion chemistry of several conductive and insulating polymers and alkali ions. The physical properties of the resulting materials is discussed.
INTRODUCTION It is well known that intercalation of organic molecules or inorganic ions into layered materials brings about dramatic changes in their properties. ' Layered metal oxides and sulfides are particularly amenable to intercalation and show a plethora of intriguing physical phenomena 2. 3 (e.g. charge density waves). Some will find applications as electrode materials in rechargeable batteries 4. 5 and electrochromic devices. 6 On the contrary, conducting polymers are amorphous and structure or property modifications cannot be readily accomplished. The systematic control and modification of the physical, structural and electronic properties of conductive polymers has only recently become an active area of research. 7 Rational and facile approaches to materials with predictable and specific properties have yet to be developed. A desirable goal in optimizing the charge transport properties of these polymers and eventually obtaining a more profound understanding of the relation between electronic and lattice structure is to prepare oriented or even crystalline polymers. From a technological viewpoint, such property modifications are desirable because they will render these materials appropriate for numerous applications such as better rechargeable high energy density battery electrodes5 ,8 and reliable components in molecular electronics. 9 ,10 Three prototype polymers, polyaniline (PANI), polypyrrole (Ppy) and polythiophene (Pth), are of particular interest partly because they are highly conductive, stable and under certain conditions can be fabricated into thin films. They are usually prepared by electrochemical or chemical oxidation of their corresponding monomers i.e. aniline, pyrrole and thiophene. Unlike
Mat. Res. Soc. Symp. Proc. Vol. 210. 01991 Materials Research Society
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electrochemical methods, chemical oxidative polymerization of these monomers always yields amorphous insoluble powders which are extremely difficult to fabricate into films. An interesting development in the chemistry of these materials is the ability to insert these polymers in layered inorganic host structures such as FeOC 1 I and V20512. This can be accomplished by the in-situ intercalation/polymerization of the monomers to yield layered materials containing monolayers of conductive polymers, inserted in the intralamellar space of the host. When intercalated, the polymers can be thought of as being ordered at least perpendicular to the stacking direction. These materials are interesting because they ar
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