本實驗所使用的p型熱電材料Bi0.4Sb1.6Te3 (BST)是以spark plasma sintering的技術來製作。與傳統的熱電塊材相比，將材料球磨(ball milling)冶金後再使用spark plasma sintering製做的試片，因燒結時間的縮短，可保持材料的奈米結構，進而提升熱電材料的熱電轉換性質。但試片在燒結過程中會受到一持續的力，造成燒結試片在平行及垂直壓力方向平面有些許不同的結構出現。界面反應中Ni-P/BST系統經退火發現，Ni-P/BST∥反應生成的NiTe IMC生長速率常數較Ni-P/BST系統快，其原因為平行及垂直壓力方向平面擴散途徑的不同，使Ni-P/BST∥中的Ni更容易與Te反應生成NiTe IMC。 BST材料的Seebeck係數在150 oC下退火，隨退火時間的增加並未出現明顯變化；但導電率卻隨退火時間而有上升再下降的趨勢。導電率變化主要受到載子濃度及遷移率所影響，載子遷移率的上升主導導電率的上升，而載子濃度的下降主導導電率的下降。另外，在Ni-P/BST/Ni-P系統中，Ni-P層對熱電材料的熱電性質也會有所影響。Ni-P層因提供大量的載子，使Ni-P/BST/Ni-P系統的有效Seebeck係數大幅度下降；但在有效導電率方面卻因Bi precipitation出現所提供的載子而隨著退火時間上升。由Seebeck係數及導電率計算power factor後發現，Ni-P層的存在雖提升了導電率，但整體而言仍然對BST材料的熱電性質有負面影響。 In this study, p-type Bi0.4Sb1.6Te3 (BST) thermoelectric material was fabricated by ball-milling and spark plasma sintering (SPS) technique. Comparing to the conventional technique samples, SPS thermoelectric materials show significant improvement of thermoelectric figure of merit (ZT) due to small grain size. The samples were surf an external compressing force during the sintering process. Thus, the structure of the surface parallel to compressing direction differed from the surface perpendicular to compressing direction. In interfacial reaction, the growth rate constant of NiTe IMC in Ni-P/BST∥ system in all aging condition were larger than in Ni-P/BST system because of the different diffusion paths of these two system. The Seebeck coefficient of BST at 150 oC aging had no obvious change with aging time. However, the conductivity increased in short time aging then decreased in long time aging. The variation of the conductivity was mainly due to the change of carrier concentration and carrier mobility, therefore, the increase of carrier mobility dominant the increase of conductivity and the decrease of carrier concentration dominant the decrease of conductivity. On the other hand, the electroless Ni-P layer also affect the thermoelectric performance of BST material. Ni-P layer provided large amount of carrier to lower the effective Seebeck coefficient in Ni-P/BST/Ni-P system. But the increase of the carrier concentration effectively increased the effective conductivity in Ni-P/BST/Ni-P system. The calculation of the power factor showed that the Ni-P layer truly decrease the electrical transport properties of BST thermoelectric material.
