n型鉍-硒-碲及p型鉍-銻-碲熱電材料之製作與研究

Abstract

找尋新穎的熱電材料是現在許多物理、化學以及材料學家的熱門研究，熱電材料的益處在於可將生活中所產生的廢熱轉化成電能再度利用，可應用在於熱機或是冷凍機之上。\n首先，在第一個研究之中，透過布理奇曼法在1050 ℃之下維持10個小時用以製作Cu0.01Bi2Te2.7Se0.3塊材，以及透過水熱法製造出Cu0.01Bi2Te2.7Se0.3奈米粒子，並且將兩種不同尺寸的粒子做不同比例的混合：奈米粒子(粒徑：20~100奈米)重量百分比0、10、20、30和100；接著探討火花電漿燒結法及奈米聚合物對熱電性質之影響。在實驗中發現材料中混入百分之三十的奈米粒子可提升熱電優質係數約一倍，由0.35提升至0.74。若是可以將起初塊材的熱電優質係數提升至較良好的0.7以上，再透過奈米聚合和燒結，其熱電係數在400 K左右是可以超過1的。由這個研究顯示出：火花電漿燒結以及奈米聚合是可以有效的提升熱電優質係數，其主要原因來自於成功的降低熱傳導係數並同時維持住原本所擁有的電阻率以及席貝克係數的提升，而熱傳導降低因於樣品中的奈米結構所造成的粒子邊界增加、晶格的不匹配導致抑制聲子的傳熱所形成的結果。\n第二個研究為一樣是透過布理奇曼法在750 ℃之下維持12個小時用以製作BixSb2-xTe3塊材，其中x分別為0.4、0.45、0.5以及0.6，本實驗主要為探討Bi的量對於BiSbTe所造成的影響。由結果中顯示x高於0.5和低於0.5所呈現的熱傳性質的趨勢有些許不同。在x為0.45的塊材中，得到本實驗中在室溫之下，最佳的熱電優質係數1.5，獲得此結果的主要原因來自於相對較低的電阻率，並可觀察到x為0.45的載子濃度高於0.4、0.5和0.6的結果，其將可以佐證x=0.45塊材的低電組率所造成的優質係數提升。

Physicists, chemists and material scientists at many major universities and research institutions throughout the world are attempting to create novel materials with high thermoelectric (TE) efficiency. It will be beneficial to harvest waste heat into electrical energy. Specialty heating and cooling are other major applications for this class of new TE materials. \nIn the first study, bulk and nanoparticles of Cu0.01Bi2Te2.7Se0.3 were prepared separately. The Cu0.01Bi2Te2.7Se0.3 bulk was fabricated by Bridgeman method at 1050 ℃ for 10 hrs and the nanoparticles were made through hydrothermal method. Two kinds of powders were mixed with the ratios of NPs 0, 10, 20, 30 and 100 wt% and sintered by the SPS technique to form the composite specimens. The ZT value can be enhanced over 100% from 0.35 to 0.74 for specimen with 30 wt% nanoparticles. The consequence indicates that the SPS process and mixing nanocomposite can effectively enhance ZT value. The enhancements were caused mainly by the presence of nanostructured regions existing within the samples which lowered the thermal conductivity. The phenomenon is due to the presence of significant number of grain boundaries, shorten phonon mean free path and lattice mismatch.\nFor another investigation, the BixSb2-xTe3 ingots with x=0.4, 0.45, 0.5 and 0.6. were fabricated by Bridgeman method at 750 ℃ for 12 hrs. We studied the effects of amount of Bi in BixSb2-xTe3 and the SPS process on the ZT enhancement. The experiment showed that for x >0.5, the thermal property changed from a curve to a relatively linear line at the end. The best ZT is 1.5 ingot at 300 K for x=0.45 specimen. The significant ZT improvement arises from the much-reduced electric resistivity. The lowest resistivity for x=0.45 specimen is mainly due to the highest carrier concentration than those with x=0.4, 0.5 and 0.6 ingots.