Novel forms of light element guests in micropores of graphitic systems: Structures, electronic states and magnetism

Carbon-based materials such as graphite and microporous carbon provide room for the accommodation of guest materials. In graphite, the galleries between graphitic sheets form a two-dimensional space available for the guest materials, while guests are accommodated in the micropore network having a random structure in the microporous carbon systems. It is expected that the guest materials in these micropore spaces, having restricted geometry and dimensionality, form different structures from the structures of the ordinary bulk states. Moreover, the guest materials, geometrically confined in the micropore state, provide novel solid state properties related to their peculiar structures. We designed novel forms of guest systems considering the structure, electronic properties and magnetism, employing light element guest materials such as He, H-2 and O-2 in alkali metal-graphite intercalation compounds and microporous activated carbon fibers. In this paper, we review the four cases investigated in our group: the two-dimensional metallic hydrogen, the two-dimensional oxygen layer, helium atoms in ultra-micropores and the random magnetic system of condensed oxygen molecules.