相對傳統的合金熱電材料而言，氧化物熱電材料在空氣環境中具有更好的化學穩定性，因而更適合於中高溫區的應用。本實驗以固態反應法合成兩種複合氧化物材料，即 BaCoO3 和 BaBiO3，探討其熱電性質，以及改變氧計量比或摻雜其他元素對熱電性質的影響。X-射綫繞射證實在 800℃ 於空氣中結燒 24 小時可得單一相之 BaCoO3。若將燒結溫度升至 900℃ 以上，樣品會形成一種缺氧的新相 BaCoO2.6，密度亦隨之減少。若再將樣品於 800℃ 退火，缺氧相會變囘 BaCoO3，證明為可逆相變。熱電測量顯示，若樣品燒結溫度為 800℃，在 BaCoO3 中摻雜鎳與鋅不僅會使電阻率降低，也會提高熱電係數。若燒結溫度為 950℃ 隨後在 800℃ 退火，雖然 X-射綫繞射顯示樣品仍為 BaCoO3 相，但摻雜鎳與鋅會使電阻率上升，熱電係數下降。前者的熱電係數在 300700K 為正值，而後者的熱電係數在 300500K 為負值，500K 以上轉變為正值，顯示有兩種類型載子共存的現象。BaCoO3 系列樣品所測得的熱電功率因數皆很低，最佳值在 973K 時僅為 23 μWm-1k-2。BaBiO3 的合成條件為 800℃ 在空氣中燒結 12 小時，隨後在 600℃ 於氧氣中退火 24 小時以降低電阻率，其數值在室溫時約為 104 cm，在 973K 降為 5.95 cm，但仍然太大而不適合於熱電應用。

Compared to the traditional thermoelectric alloys, oxide thermoelectrics have a better chemical stability in air and therefore are better suited for the applications in the mid to high temperature regions. In this thesis, two complex oxides, i.e. BaCoO3 and BaBiO3, were synthesized by the solid state reaction method and their potentials as the thermoelectric material were investigated. The influence of the oxygen stoichiometry and doping of other elements were also studied. X-ray diffraction (XRD) indicated that the BaCoO3 samples sintered at 800 C in air for 24 hrs had a pure phase. If the sintering temperature was raised to 900 C, an oxygen deficient phase, i.e. BaCoO2.6, was formed with a reduced density. The BaCoO3 phase could be recovered after the oxygen deficient phase was annealed at 800 C, indicating that the phase transition was reversible. Thermoelectric measurements showed that if the samples were prepared at 800 C, Ni or Zn doping would result in a decrease in electrical resistivity but an increase in Seebeck coefficient, however, if the samples were sintered at 900 C followed by annealing at 800 C, the Ni or Zn doping would result in opposite results although XRD indicated that both samples had the same BaCoO3 phase. The 800 C sintered samples had positive Seebeck coefficients at 300700 K, while the Seebeck coefficients of the 800 C annealed samples showed negative values at 300500 K and then turned into positive values over 500 K, indicating the coexistence of both types of charge carriers. All the BaCoO3 samples showed small power factors with the highest value of 23 Wm-1K-2. The BaBiO3 samples of a pure phase were sintered in air at 800 C for 12 hrs, followed by annealing at 600 C in oxygen for 24 hrs to decrease the electrical resistivity, which had the values of 104 cm at room temperature and 5.95 cm at 973 K that were far too large for the thermoelectric application.

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