Vertical Bridgman growth of thermoelectric clathrate Ba8Ga16Sn30 with a type-VIII structure

Abstract

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 Ba8Ga16Sn30 and p-type Ba8Ga16Sn30−xGex (x≈0.7) are 10mm 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 9μW/K2cm, respectively, for n- and p-type crystals.