ICT2014 Abstracts

The conditions of crystal growth of type-VIII clathrate Ba₈Ga₁₆Sn₃₀ (BGS) have been studied by combining differential thermal analysis (DTA) and power X-ray diffraction (XRD) analysis on samples with various compositions. It is found that the type-VIII BGS is formed when the raw materials were heated above 465℃. After the samples were heated to 910℃above the melting point at 495℃, an exothermic peak was observed in the cooling process at 611 - 654℃depending on the BGS/Ga ratio. This observation indicates the presence of a liquidus line above the peritectic point of BGS at 495℃, which is at variance with the congruent melt of BGS previously reported.       

Based on the revised phase diagram between Sn, BGS, and Ba(Ga/Sn)₄, the vertical Bridgman method was applied to grow single crystals of n-type and p-type by tuning the initial composition and temperature program. Both n-type Ba₈Ga₁₆Sn₃₀ and p-type Ba₈Ga₁₆Sn_30-xGe_x (x ≈ 0.5) crystals of 10 mm in diameter were grown at the bottom of quartz ampoules. The value of Seebeck coefficient and electrical resistivity weakly change along the vertical direction of the as grown crystals, whereas, the thermoelectric powder factor showed no significant gradient.