Regensburg 2007 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 20: Poster session
MM 20.39: Poster
Dienstag, 27. März 2007, 14:45–18:00, Poster C
Electric field gradient and chemical bonding in intermetallic gallides — •Katrin Koch1, Frank Haarmann1, Klaus Koepernik1,2, and Helge Rosner1 — 1MPI CPfS, Dresden, Germany — 2IFW, Dresden, Germany
The understanding of the metallic bond is still a challenging
task. Here, we investigate experimentally and theoretically
two series of compounds: the hexagonal MGa2 with M=Ca,Sr,Ba and the
tetragonal MGa4 with M=Na,Sr,Ba. Ga forms a planar network
of 3-fold coordinated atoms in MGa2. In MGa4 a 3-dimensional
network of 4- and 5-fold coordinated Ga atoms is formed.
The different bonding situations in these compounds indicate a flexibility
of Ga with respect to the chemical bonding. We present a study of the
electrical field gradient (EFG) for the different Ga sites in these
materials. The quadrupolar coupling constants were measured by NMR, and
the EFG was calculated using a DFT band structure code (WIEN2k).
In comparison, the results of our calculation allow a unique
assignment of the different signals to specific Ga sites. In addition,
the calculations reveal that the EFG is very sensitive to internal
structural parameters. For the optimized Ga positions (with respect to
the total energy) we find excellent agreement of the measured and
calculated EFG values.
The large quadrupole coupling constants indicate
clearly the covalent nature of the
Ga bonds.
Studying in detail the influence of the cations
using the virtual crystal approximation we show that a simple point
charge model can not be applied for this family of covalent metals.
The DFG SPP 1178 is acknowledged for financial support.