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RESEARCH PRODUCT

Valence instabilities and inhomogeneous mixed valence in some ternary europium compounds

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Abstract Photoemission spectra and TB-LMTO-ASA band structure calculations of some mixed valency europium compounds hve been studied. The band structures are compared with the band structures of the isostructural lanthanum and strontium compounds. Surprisingly a 4f density of states in the vicinity of the Fermi level is observed in inhomogenous mixed valency EuPd 3 B, Eu 3 S 4 , and EuPdP. Indeed a van Hove Singularity (vHS) derived from the d states of La and Pd or p states of boron or phosphorous are found in La 3 S 4 , LaPd 3 B and SrPdP. The valence instability in the Eu compounds is thus not necessarily due to Eu 4f states. The results also provide some ground for the assumption that inhomogeneous mixed valency is an indicator for a vHS in the conduction band. The europium compounds order anti-ferromagnetically at low temperatures. whereas La 3 S 4 becomes superconducting at 8 K. In La 3 S 4 , the vHS coincides with the Fermi level, whereas the singularity lies below the Fermi level in SrPdP and LaPd 3 B. According to the van Hove scenario it must be possible to induce superconductivity via hole doping in SrPdP and LaPd 3 B.