3 research outputs found
Electronic structure and bonding of the metal cluster compound Au55(PPh3)12Cl6
We discuss the electronic structure, bonding and physical properties of the gold cluster compound Au55(PPh3)12Cl6. Results from our experimental measurements, including EXAFS, specific heat, Mossbauer, UV-visible and photoelectron spectroscopy, are combined with those of other work to form a consistent physical picture of the system. The bonding in Au55(PPh3)12Cl6 is much more delocalised and non-directional than in smaller gold cluster molecules. The Au55 cluster exhibits a substantial degree of metallic bonding, while displaying some of the characteristics of a discrete energy level spectrum
Wüstite: electric, thermodynamic and optical properties of FeO
We report on a systematic optical investigation of w\"ustite. In addition,
the sample under consideration, Fe0.93O, has been characterized in detail by
electrical transport, dielectric, magnetic and thermodynamic measurements. From
infrared reflectivity experiments, phonon properties, Drude-like conductivity
contributions and electronic transitions have been systematically investigated.
The phonon modes reveal a clear splitting below the antiferromagnetic ordering
temperature, similar to observations in other transition-metal monoxides and in
spinel compounds which have been explained in terms of a spin-driven
Jahn-Teller effect. The electronic transitions can best be described assuming a
crystal-field parameter Dq = 750 cm-1 and a spin-orbit coupling constant
\lambda = 95 cm-1. A well defined crystal field excitation at low temperatures
reveals significant broadening on increasing temperature with an overall
transfer of optical weight into dc conductivity contributions. This fact seems
to indicate a melting of the on-site excitation into a Drude behavior of
delocalized charge carriers. The optical band gap in w\"ustite is close to 1.0
eV at room temperature. With decreasing temperatures and passing the magnetic
phase transition we have detected a strong blue shift of the
correlation-induced band edge, which amounts more than 15% and has been rarely
observed in antiferromagnets.Comment: 13 pages, 10 figure