Abstract Scope |
Clathrate, or ‘cage and rattler,’ thermoelectric materials are promising candidates for high-efficiency thermoelectricity, offering low thermal conductivities. Barium germanide clathrates have been synthesized in previous studies with moderate efficiencies, with some articles showing that Yb-doping reduces thermal conductivity. However, the doping mechanism has not been clarified yet. Here, six (6) bulk samples of barium germanide clathrate were synthesized, substituting small amounts of ytterbium into the barium stoichiometry. Upon x-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and thermoelectric analysis, the solubility of Yb into the Ba site was found to be around 1.6%, with most Yb atoms precipitated as a secondary phase. The SEM revealed that the secondary phase was distributed around the grain boundaries as small particles with sub-micrometer sizes, which was the main reason for reduced thermal conductivity. As a result, about 10% increased thermoelectric figure of merit, ZT, was observed by the Yb doping. |