Bi3(Nb1-xMx)O7-δ (M = Mg, Ho) 的製備與離子導電性研究

Preparation and ionic Conductivity of Bi3(Nb1-xMx)O7-δ (M = Mg, Ho)

施長志(Chang-Chi Shih)

指導教授 ： 高惠春

淡江大學/理學院/化學學系碩士班/碩士(2012年)

https://doi.org/10.6846/TKU.2012.00959

摘要

本實驗採用固態法製備Bi3(Nb1-xMgx)O7-1.5x (x = 0-0.70)和Bi3(Nb1-xHox)O7-x (x = 0-1.0)兩系列樣品，在空氣中熱處理溫度分別為900 和 1000C。所有的樣品皆為螢石結構，皆有95%以上的緻密度。樣品的單位晶胞a-軸遵守Vegard定律。Ho2O3可完全溶於Bi3NbO7，而MgO卻只能溶到0.70，推論維持單相螢石結構，氧原子數必須達6以上，當MgO取代到0.70時，氧原子計量只剩5.95。以3價的Ho3+或2價的Mg2+取代5價的Nb5+，隨著取代量的增加，使得氧空缺濃度增加，有利於氧離子導電。在Bi3(Nb1-xMgx)O7-1.5x系列中，700C時，Bi3(Nb0.3Mg0.6)O6.1樣品有最高的導電度，達1.13(3) × 10-1 S•cm-1，氧離子遷移率0.881(7)，活化能0.682(7) eV。在Bi3(Nb1-xHox)O7-x系列中，700C時，Bi3HoO7樣品有最高的導電度，6.25(9) × 10-2 S•cm-1，氧離子遷移率0.872(2)，活化能0.94(1) eV。氧離子遷移率隨著溫度的升高而增加，估計在900C左右，可以接近1。假使要將這些化合物放在SOFC中當作電解質使用，建議要在900C。

關鍵字

離子導體 ； 固態電解質 ； 螢石

並列摘要

Two series of Bi3(Nb1-xMgx)O7-1.5x (x = 0-0.70) and Bi3(Nb1-xHox)O7-x (x = 0-1.0) samples were prepared by a solid state reaction method at 900 and 1000C, respectively under the static air atmosphere. The resulting samples have relative densities larger than 95% and a fluorite crystalline phase. Unit cell a-axis of them obeys Vegard’s law well. Solubility of Ho2O3 in the Bi3NbO7 is complete, but only 0.70 of the MgO can be dissolved into Bi3NbO7. It probably relates to the amount of oxygen vacancies. When x ＞0.70, the oxygen stoichiometry for the Bi3(Nb0.3Mg0.7)O5.95 is＜5.95, which may be too less to keep a fluorite phase. Substitution of Nb by Mg or Ho, both oxygen vacancies and ionic conductivity of Bi3(Nb1-xMx)O7-x is increased with increasing the amount of x. For the Bi3(Nb1-xMgx)O7-1.5x series, at 700C, x = 0.60 has the highest conductivity, 1.13(3) × 10-1 S•cm-1 with a transference number of 0.881(7) and the least activation energy of 0.682(7) eV. For the Bi3(Nb1-xHox)O7-x series, at 700C, Bi3HoO7 has the highest conductivity 6.25(9) × 10-2 S•cm-1 with a transference number of 0.872(2) and the least activation energy of 0.94(1) eV. Transference number increases with increasing the measuring temperature, in order to obtain a transference number close to 1, for the pure ionic conduction as an electrolyte in the SOFC, these bismuthate may be used at temperature close to 900C.

並列關鍵字

ionic conductivity ； solid state electrolyte ； fluorite ； crystal structure ； solid oxide fuel cell

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