Interrelations between atomic and electronic structures—Liquid and amorphous metals as model systems

Abstract

In this paper we review an intimate interrelationship between atomic and electronic structures. Charge- and spin-density oscillations in the electron system, giving rise to so-called Friedel and RKKY oscillations in the effective pair potential or the effective magnetic interaction, cause indirect ion-ion and spin-spin interactions mediated by the conduction electrons. These interactions prefer positions of neighbouring ions and local moments which are commensurate with their minima and/or maxima. Structure itself has a strong influence on the electronic states. Structure-induced gaps in the electronic density of states occur at Brillouin-zone boundaries. Whereas for crystalline systems these interrelations are well established, they are still controversial for disordered systems. In this paper we discuss non-magnetic as well as magnetic amorphous glasses and liquid alloys. We will show that due to their isotropy the electron-structure interrelationships are observed even more easily than in crystalline systems. The systems under consideration may serve as models for electron-structure interrelationships and show many similarities to an isotropic three-dimensional Peierls system. After reviewing the electronic influence on structure, we mainly focus our attention on photoelectron spectroscopy of the UPS region. These measurements clearly show structure-induced pseudogaps in the electronic density of states. Concentration and temperature dependences are in good agreement with theory. One pseudogap is far below E F and hence unimportant for most properties. Another one is at E F, with strong influences on electronic transport and phase stability. The relation of the pseudogap at E F in non-magnetic alloys to the glass-forming ability, the thermal stability, and deviations of electronic transport properties from the free-electron behaviour are reported. The resistivity, the Hall coefficient and a new interpretation of the thermopower are discussed in some detail. Influences of the indirect magnetic interaction on the thermal stability, the atomic structure, and the magnetic behaviour are also briefly discussed.