Synthesis, Structure And Low-temperature Oxygen Ionic Conducting Properties Of Bi₂Me_0.1V_0.9O_5.5-δ(Me=Co, Cu) Compounds

Aurivillius phase structure of Bi₂Me_0.1V_0.9O_5.5-δ(Me=Co, Cu) compositions have received increasing attention in recent years due to their superior oxygen ionic conducting properties at 300-600℃, making them promising candidate materials for many important applications, such as oxygen separation membranes, membrane reactors and oxygen sensor devices. In the present dissertation, an' EDTA-citrate process was adopted to synthesize Bi₂Me_0.1V_0.9O_5.5-δ and Bi₂Me_0.1V_0.9O_5.5-δ oxides. The synthesis and preparation, microstructural characteristics, sintering properties, order-disorder phase transition and oxygen ionic conducting properties of Bi₂Me_0.1V_0.9O_5.5-δ(Me=Co, Cu) oxides have been investigated. The oxygen ionic conducting properties have been interpreted with respect to microstructure and the order-disorder phase transition.Bi₂Me_0.1V_0.9O_5.5-δ(Me=Co, Cu) fine powders have been synthesized by the EDTA-citrate method. TG-DSC measurement was employed to analyze the formation process of Aurivillius structure as a function of temperature. The phase purity and morphology of synthesized powders have been examined by XRD and SEM, respectively. The preferred synthesis conditions were ascertained based on above mentioned research.The sintering properties of Bi₂Me_0.1V_0.9O_5.5-δ(Me=Co, Cu) ceramics were evaluated by XRD, SEM, thermal dilatometer measurement and ac impedance spectroscopy. An obvious influence of microstructure on oxygen ionic conducting properties has been detected for the ceramics. It was found that sintering temperature plays an crucial role in determining the microstructure feature and oxygen ionic conductivity of the ceramic, while the effect of sintering time on the microstructure and oxygen ionic conducting properties is insignificant. Sintering at 640℃ for 1-3h was ascertain to be preferred, yielding dense microstructure with fine and uniform grains and high oxygen ionic conducting properties.The order-disorder phase transition in Bi₂Me_0.1V_0.9O_5.5-δ(Me=Co, Cu) ceramics were characterized by DSC, linear thermal expansion measurement and ac impedance spectroscopy. During a heating/cooling cycle, a reversible order-disorder phase transition was observed in Bi₂Me_0.1V_0.9O_5.5-δ(Me=Co, Cu). The ceramics prepared by the EDTA-citrate method display arather faint hysteresis in oxygen ionic conductivity during the heating/cooling cycle compared with the specimens prepared by the conventional solid state method. It was considered that the desired microstructure feature of the ceramics prepared by the EDTA-citrate method is responsible for the depressed hysteresis in oxygen ionic conductivity during the heating/cooling cycle.