A new view of valence instabilities in europium compounds: van Hove singularity in EuPdP

¹ Max-Planck Institut für Festkörperforschung, D-70506 Stuttgart, Germany
² Institut für Elektronische Eigenschaften Forschungszentrum, D-52425 Jülich, Germany
³ Institut für Anorganische Chemie und Strukturchemie II, Heinrich-Heine-Universität, D-40225 Düsseldorf, Germany
⁴ Institut für Physikalische Chemie II Universität zu Köln, D-50939 Köln, Germany

Received: 18 March 1997
Accepted: 18 August 1997

Abstract

Photoemission spectra and the TB-LMTO-ASA band structure of the mixed valent europium compound EuPdP (ZrBeSi type structure) were studied and compared with the results obtained on isostructural SrPdP and EuAuAs and the -type compound . is a homogeneous mixed valent compound, whereas the situation in EuPdP is not clear. The Mössbauer spectroscopy suggests static mixed valency in EuPdP corresponding to partially localized electrons, but from the photoemission measurement we know that the situation in EuPdP is different from the static mixed valent . Band structure calculations as well as photoemission spectra indicate a density of states in the vicinity of the Fermi level in EuPdP, which belongs to a van Hove Singularity (vHS). In EuPdP we therefore expect homogeneous mixed valence, similar to with itinerant electrons. The absence of homogeneous mixed valence is possibly associated with the layered structure of EuPdP, enabling charge ordering through a Martensitic phase transition. A high density of states associated with a singularity at the Fermi energy seems to be responsible for the structural instability in inhomogeneous mixed valent europium compounds.