Rattling of Ba-atoms in Ba8ZnxGe43-5x/8([]3-3x/8)

Full text: In order to improve the figure of merit of thermoelectric materials, one of the key parameters to be minimized is the lattice thermal conductivity. It is thus essential for the design of new thermoelectric materials to understand the lattice dynamics, especially the scattering mechanism of low energy phonons. The present paper describes formation, phase relations at subsolidus temperatures as well as at 800 oC, crystal chemistry and physical properties of a series of ternary clathrates as part of the solid solution, Ba8Znx(Ge43-5x/8[]3-3x/8), deriving from binary Ba8Ge43[]3 with a solubility limit of 8 Zn per formula unit at 800 oC. Structural investigations in all cases confirm cubic primitive symmetry with a lattice parameter a ∼ 1.1 nm consistent with the space group type Pm-3n. Studies of transport coefficients evidence electrons as the majority charge carriers in the systems. Thermal conductivity exhibits a pronounced low temperature maximum, dominated by the lattice contribution, while at higher temperatures the electronic part gains weight. Inelastic neutron scattering experiments are used to study the phonon spectrum for Ba8Zn8Ge38. (author)