Synthesis And Characterization Of La_9.33Ge₆O₂₆ Electrolyte And Its Co Doping On Ge Site

With the growing concerns regarding increasing greenhouse gas emissions and their effect on climate change,there has been substantial interest in the demonstration and utilization of solid oxide fuel cell?SOFC?systems.Recently,apatite-type lanthanum germanates have attracted considerable interest as promising electrolytes due to their high oxide ion conductivities(>0.01 S?cm^-1)and low activation energy?<1 eV?in a reduced atmosphere at intermediate temperature?IT??500–800 ??.In addition,studies on lanthanum germanates have become a hot topic in science,because it is crucial to understand the characters and formation of different phases of these systems.In this thesis,we put research contents focus on the preparation and characterization of apatite-type La_9.33Ge₆O₂₆ electrolyte and its Co doping on Ge site.Oxyapatite powders La_9.33+x/3Ge_6-xCo_xO26?0?x?0.8?are directly synthesized via molten-salt method that using LiCl/NaCl?the mass ratio of LiCl and NaCl is 1:1?as eutectic salt on the properly selected reaction conditions?eutectic salt,sintering temperature,and so on?.By researching the effect on the conductivity of Co doping on Ge sites,we confirm the threshold and optimal value of Co dopant.The experiment results show that: the oxide ion conductivity increases with Co content up to a maximum value for x=0.2,before decreasing with further Co incorporation;LaCoO₃ appears when x?0.5,indicating Co dopant threshold value for x=0.4;Co doping on Ge site leads to obvious lattice expansion and conduction channels enlargement by the reason of ionic radius of Co3+ is greater than Ge4+,enhancing oxide ion conductivity;La_9.4Ge_5.8Co_0.2O₂₆ has the largest area of oxide-ion-channel-triangular,and expresses the highest conductivity value of 1.68?10-2Scm^-1 at 750?,indicating Co dopant optimal value for x=0.2.The La_9.33Ge₆O₂₆ powders are prepared with solid LiCl as catalyst at low temperature 550-600? by salt catalyzed synthesis method,and the structure,morphology and electrical properties are discussed.The experiment results show that: pure preparation temperature of apatite-type La_9.33Ge₆O₂₆ powders can be obtained at relatively low temperature as compared to the conventional method,not only decreasing sintering temperature,but also providing a novel route of La_9.33Ge₆O₂₆ powder preparation;the dense La_9.33Ge₆O₂₆ ceramics are made by sintering at 1000?,avoiding the loss of Ge;La_9.33Ge₆O₂₆ ceramic shows excellent conductivity,the value of 1.34?10-2Scm^-1 at 750?.