Vertical Bridgman growth of thermoelectric clathrate Ba₈Ga₁₆Sn₃₀with a type-VIII structure

Type-VIII clathrate Ba₈Ga₁₆Sn₃₀(BGS) is a promising thermoelectric material with tunable carrier types. We have studied the Bridgman growth conditions by combining differential thermal analysis (DTA) and powder X-ray diffraction analysis. It is found that the raw elements Ba, Ga, and Sn react at 465 °C to form the type-VIII BGS compound. The DTA indicates the presence of a liquidus line above the peritectic point of BGS at 495 °C. By using the vertical Bridgman method, single crystals of n-type and p-type BGS have been grown from Sn-rich and Ga-rich initial compositions, respectively. The obtained crystals of n-type Ba₈Ga₁₆Sn₃₀and p-type Ba₈Ga₁₆Sn_30-xGe_x(x≈0.7) are 10 mm sized. On several parts cut from the grown crystals, the Seebeck coefficient and electrical resistivity have been measured up to 330 °C. The values weakly change along the vertical direction of the crystals, keeping the thermoelectric power factors as high as 12 and 9 μW/K²cm, respectively, for n- and p-type crystals.