Metallic state in a lime-alumina compound with nanoporous structure.

We report a metallic state in a nanostructured porous crystal 12CaO x 7Al2O3 by incorporating electrons in the inherent subnanometer-sized cages, in which a three-dimensionally closely packed cage structure acts as an electronic conduction path. High-density electron doping ( approximately 2 x 10(21) cm(-3)), which was achieved by a thermal treatment in Ti metal vapor at approximately 1100 degrees C, induces homogenization of the cage geometry to a symmetric state, resulting in an insulator-metal transition with a sharp enhancement of the electron drift mobility from approximately 0.1 to 4 cm(2) V(-1) s(-1). The results provide an approach for the realization of electroactive functions in materials composed only of environmentally benign elements by utilizing the appropriate nanostructures.