Metallic behavior of the Zintl phase EuGe2:: combined structural studies, property measurements, and electronic structure calculations

The Zintl compound EuGe2 crystallizes in the trigonal space group P (3) over bar ml (No. 164) with the CeCd2-structure type. Its structure can be formally derived from the hexagonal AIB(2)-structure type by a strong puckering of the hexagonal layers. The chemical bonding in EuGe2 can be rationalized according to the Zintl concept as (Eu2+)(Ge1-)(2), since the europium atoms are divalent and each germanium atom receives one additional valence electron. In that sense, EuGe2 is expected to be a closed-shell compound with semiconducting behavior. However, temperature dependent resistivity measurements show EuGe2 to be metallic. Subsequently, detailed crystallographic studies revealed the structure and the composition of EuGe2 to be free of defects and impurities, which, along with the confirmed divalent oxidation state of the europium atoms by means of magnetic measurements, make EuGe2 another example of a metallic Zintl phase. These results are in good agreement with the results of electronic structure calculations such as TB-LMTO-ASA (LDA) and FLAPW (GGA), which reveal non-zero DOS at the Fermi level. (C) 2004 Elsevier Inc. All rights reserved.