Preparation And Characterization Of Bi₂O₃/YSZ And Bi₂O₃/YbSZ Electrolytes

Due to its good high-temperature electrical conductivity, thermal and chemical stability, solid ionic electrolytes based on zirconia have been used widely as materials of oxygen sensors at high temperature. However, the conductivity of these materials at low temperature is not high enough and therefore the application at low temperature is limited. Moreover, the sintering of these materials always needs high sintering temperature, consuming more energy.In order to improve the conductivity of these materials at low temperature and decrease the sintering temperature, we prepared co-doped zirconia composed of Bi2O3 with yttria stabilized zirconia (Bi2O3/YSZ), and Bi2O3 with ytterbium stabilized zirconia (Bi2O3/YbSZ), respectively by the solid state reaction methord. The phase, morphology, structure and electrical property of these electrolytes were studied by X-ray diffraction, electron microscopy and ac impedance spectroscopy.Results indicate that the addition of Bi2O3 has a dual function:First, because the low melting point of Bi2O3, it effectively promotes the sintering process, making it possible to get uniform, dense and fully stabilized cubic zirconia at low sintering temperature (1200-1300℃); Second, with the addition of 2mol% Bi2O3, the conductivity of 10YSZ (10mol% Y2O3 stabilized zirconia) and lOYbSZ (10mol% Yb2O3 stabilized zirconia) improve to twice and 1.3 times of the maximum conductivity of electrolytes without Bi2O3 in YSZ and YbSZ, respectively.The characterization and analyses of ac impedance technology combined with transmission electron microscopy indicate that a part of the Bi2O3 dissolves in the grains of zirconia and improves the grain conductivity. Other Bi2O3 segregates at grain boundaries, clearing the impurities and connecting the transport channels for oxygen ions and therefore increases the conductivity of grain boundary effectively.