2:30 PM–5:30 PM, Monday, March 10, 2008
Morial Convention Center - 230
Sponsoring Unit:
DCMP
Chair: George M. Stocks, Oak Ridge National Laboratory
Abstract ID: BAPS.2008.MAR.D38.15
5:18 PM–5:30 PM
Emmanuel Nenghabi
(Texas Tech Univeristy)
Charles Myles
(Texas Tech University)
The type I clathrate lattice is simple cubic with 46 atoms per unit cell. The cages in this lattice can host ``guests'' and the framework can have substituted atoms. Here, we focus on the ``alloy'' system Ba$_{8}$Al$_{x}$Ge$_{30-x}$ (x is an integer; 0$<$x$<$15). The Ba are guests and Al substitutes for some Ge framework atoms. Using the local density approximation (LDA), we have calculated some properties of the type I clathrates Ba$_{8}$Al$_{13}$Ge$_{33}$ and Ba$_{8}$Al$_{16}$Ge$_{30}$. Our calculations of the equilibrium structures predict that Ba$_{8}$Al$_{16}$Ge$_{30 }$and Ba$_{8}$Al$_{13}$Ge$_{33}$ have approximately the same lattice constant and that Ba$_{8}$Al$_{13}$Ge$_{33}$ is expected to be slightly more stable than Ba$_{8}$Al$_{16}$Ge$_{30}$. Our band structures and electronic density of states results predict that Ba$_{8}$Al$_{13}$Ge$_{33}$ is metallic and that Ba$_{8}$Al$_{16}$Ge$_{30}$ is a semiconductor with an indirect fundamental band gap of 0.3 eV. The vibrational spectrum predicts low frequency rattling modes caused by the Ba guests that are loosely bound in the Al-Ge framework cages. Such modes may scatter the heat-carrying acoustic vibrational framework modes, potentially reducing the thermal conductivity.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2008.MAR.D38.15