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

• Main Authors: Chang-Chi Shih, 施長志
• Other Authors: Huey-Chuen I. Kao
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/80330946917587012681

碩士 === 淡江大學 === 化學學系碩士班 === 100 === 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.