Metal-Insulator Transitions

Abstract

Several kinds of metal-insulator transitions are discussed. In non-crystalline systems a second order “Anderson” transition can be described without considering electron-electron interaction. In crystalline systems, we describe band-crossing transitions and “Mott” transitions, both of which should show a discontinuity in the number of carriers when electron-electron interaction is included. The difficulty of observing this directly is stressed. Sufficient disorder in the system will remove the discontinuity. Fluid caesium, metal-ammonia and expanded fluid mercury are contrasted with Si:P. Some crystalline compounds of transition metals Ti2O3, VO2, V2O3, NiS2 and NiS are described, each of which seems to involve its own different mechanism. A new suggestion is made for Ti2O3. One other kind of transition is brieflymentioned, the Verwey transitions in Fe3O4. © IUPAC