High temperature thermoelectric transport properties of double-atom-filled clathrate compounds YbxBa8-xGa16Ge30

Type-I clathrates YbxBa8-xGa16Ge30 (x=0-1.3) filled by ytterbium and barium were synthesized by melting reaction method combined with spark plasma sintering method. The structure and thermoelectric properties of double-atoms-filled clathrate compounds are investigated. X-ray diffraction patterns and Rietveld analysis reveal that the compounds prepared by this method are type-I clathrates. The filling atoms exhibit atomic displacement parameters that are larger than that of framework atoms. All specimens show n-type conduction and the room temperature carrier concentration (N-p) increases with the increasing Yb content. The electrical conductivity of the compounds increases at first and then decreases with the increasing Yb content. When x=0.7, it reaches the maximum. The Seebeck coefficient decreases gradually with the increasing x. The substituting of Yb atoms for Ba leads to significant influence on the lattice thermal conductivity of the compounds. The lattice thermal conductivity decreases gradually with the increasing x. Of all the YbxBa8-xGa16Ge30 compounds, Yb0.5Ba7.5Ga16Ge30 compound has the greatest ZT value and its maximal ZT value reaches 1.1 at about 950 K. Compared with the Ba8Ga16Ge30 sample, it increases by 90% at the same temperature. (c) 2008 American Institute of Physics.