1. A memristive element (M) formed by: a first electrode; a second electrode; and an active region consisting of a thin film of an insertion compound of at least one alkali metal, made of an oxide or chalcogenide of at least one transition metal, exhibiting conductivity that is both electronic and ionic in nature, said active region making direct electrical contact with said first and second electrodes, wherein said first electrode is a surface of a degenerate semiconductor substrate.