Characterization of electrons in solids by structure I. Localized vs collective electrons
1967; Elsevier BV; Volume: 2; Issue: 1 Linguagem: Inglês
10.1016/0025-5408(67)90041-4
ISSN1873-4227
Autores Tópico(s)Solid-state spectroscopy and crystallography
ResumoAbstract Outer d electrons in solids may be either localized or collective, depending upon the magnitudes of the overlap integrals Δ for crystal-field orbitals on neighboring atoms. If Δ Δ c , they are localized; and if Δ > Δ c , they are collective. At Δ c there is a change from one electronic phase to the other. This change may be first-order. The crystal-field orbitals contain covalent mixing into atomic d orbitals of s and p orbitals of nearest-neighbor anions and cations, so that there are two types of overlap integrals: cation-cation Δ cc and cation-anion-cation Δ cac . If Δ cc > Δ c and Δ cac Δ c , the d orbitals form cation-sublattice band states. If Δ cc Δ c and Δ cac > Δ c , they form crystalline band states. In the case of heavy atoms in a low valence state, such as Pb2+ or Bi3+, anion-vacancy trap orbitals may mix with heavy-atom core orbitals to produce partially filled band orbitals that must be distinguished from collective d orbitals. Collective electrons in partially filled bands have a well defined Fermi surface, localized electrons do not. Therefore a Fermi-surface-dependent property that is enhanced as the band narrows and is different for localized electrons, where the Fermi surface is not well defined, is particularly useful for characterizing the state of the d electrons. Spontaneous crystallographic distortions to lower symmetry at lower temperatures represent such a property.
Referência(s)