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Abstract:
The series of ternary Eu-pnictides EuPd1-xAgxP and EuPd1-xAuxAs were
synthesized by heating the elements and characterized by means of X-ray
powder diffraction. The unusual behaviour of the lattice constants are
explained by geometric and electronic factors, in particular the change
of the Eu valence. In EuPdP and EuPdAs, the Eu atoms adopt a
temperature-dependent mixed valent state which tends towards divalency
while substituting Pd by Ag or Au. This is investigated by means of
temperature-dependent X-ray diffraction, TB-LMTO-ASA band structure
calculations and resonant photoemission (PE) experiments using
synchrotron radiation. The calculated density of states (DOS) was
compared with the results of the PE experiments. The measured partial
DOS, as well as the LMTO-DOS, of EuPdP is marked by a high DOS at the
Fermi level. A van Hove singularity in the band structure leads to a
logarithmic DOS-peak. If the Fermi level coincides with this peak,
valence instabilities are expected. The results of the LMTO band
calculations are in good agreement with the experimental facts, leading
to the conclusion that the range of valence instabilities of europium is
limited to x<0.4 in EuPd1-xAgxP and x<0.15 in EuPd1-xAuxAs.
