ICT2014 Abstracts

P-type polycrystalline Ba₈Ga₁₆Ge₃₀ type I clathrates were prepared by means of the vertical Bridgeman method. The composition of raw materials was varied to obtain crystal with three different Ga/Ge ratios. The composition and crystal structure of the Ba₈Ga₁₆Ge₃₀ clathrates were respectively determined by electron probe microanalysis and X-ray diffraction. The Seebeck coefficient and electrical conductivity were measured by an in-house apparatus from room temperature to 600°C, while the thermal conductivity was measured by laser flash method up to 550°C. It was found that the sample with Ga/Ge = 0.578 has the optimal dimensionless figure-of-merit of 1.57 at 550°C. The Ba₈Ga₁₆Ge₃₀ clathrate with the optimal ZT possesses a moderate carrier concentration but the highest carrier mobility among the three conditions. While the power factor of the Ba₈Ga₁₆Ge₃₀ sample with the optimal ZT is similar with literature data for single crystal, the lowering of its thermal conductivity in this study plays the key role in improving ZT.