ELECTRONIC-PROPERTIES OF LOW DIMENSIONAL SOLIDS - THE PHYSICS AND CHEMISTRY OF LAYER TYPE TRANSITION-METAL DICHALCOGENIDES AND THEIR INTERCALATE COMPLEXES

The electronic, magnetic, and vibrational properties of pure and intercalate complexes of the layer type transition metal dichalcogenides such as ZrS2, NbSe2 and MoS2, will be discussed in relation to their highly anisotropic or "two-dimensional" character. The phenomena to be touched on will include optical and transport properties including fast ion conduction, superconductivity, staging, magnetic properties and metal insulator transitions. Similarities to the high temperature superconductors will also be suggested. By intercalating with electron donors such as organic nitrogen containing molecules or alkali metals, it is possible to fine tune the electron occupation of a relatively narrow "d" band, and dramatically change the electronic properties. Solids such as TaS2 undergo a "Peierls" distortion, and intercalation sets up random potentials to bring about a reduction in the density of states at the Fermi level, and this results in electron localisation and variable range hopping. Similar effects can in fact also be seen in "one-dimensional" systems such as polyacetylene. Possible practical applications will be discussed, including high energy density batteries, and in particular the role of the amorphous polymer phase in the solid electrolyte, polyethylene oxide-lithium triflate, will be mentioned. © 1990.