Preparation And Properties Of W,Nb And Si Modified Lanthanum Molybdate-based Oxygen Ion Conductor

A new type of lanthanum molybdate（La₂Mo₂O₉）has been studied extensively due to its excellent electrochemical properties.At high temperaturesβ-La₂Mo₂O₉ toα-The structural change of La₂Mo₂O₉ leads to a decrease in electrical conductivity.Therefore,in order to improve electrical conductivity,it is necessary to suppress the structural phase transition of La₂Mo₂O₉.Therefore,this article mainly studies the dual doping of La and Mo sites in La₂Mo₂O₉ to suppress the structural phase transition of La₂Mo₂O₉,and studies whether the electrical conductivity has improved through the microstructure,density,and conductivity of the electron microscope.The main research contents are as follows:Preparation of La_1.7Sm_0.3Mo_2-xNb_xO₉ by Solid Phase Method（x=0.1-0.6）Electrolyte powder is pressed and sintered into a ceramic sheet,recorded as LSMN.La_1.7Sm_0.3Mo₂O₉ electrolyte powder was prepared by the sol gel method and pressed into ceramic chips,which was recorded as LSM:La_1.7Sm_0.3Mo_2-xW_xO_9-δ（x=0.1-0.6）,the electrolyte powder is pressed and sintered into a ceramic sheet,recorded as LSMW:La_1.7Sm_0.3Mo_2-xSi_xO_9-δ（x=0.05-0.5）Electrolyte powder is pressed and sintered into a ceramic sheet,which is recorded as LSMS.XRD phase analysis shows that it can be completely suppressed between room temperature and 800℃βPhase to phaseαThe structural transformation of the phase.Through density analysis,it is known that when the Nb doping amount is x=0.4,the highest density is 97.6%,and the conductivity isσ=3.05×10^-2S·cm^-1,activation energy Ea=1.723e V;When the W doping amount is x=0.2,the highest density is 98.3%,and the conductivity isσ=3.91x10^-2 S·cm^-1,activation energy Ea=1.702e V;When the Si doping amount is x=0.1,the best density is 94.8%,and the conductivity isσ=1.82x10^-2S·cm^-1,activation energy Ea=1.909e V.It can be seen that W doping has the best density,with the highest density reaching 98.3%when the W doping amount x=0.2 and the sintering temperature is 800℃.Under medium to low temperature conditions,it has good electrical conductivity andσ_LSMW0.2=0.0391S·cm^-1>σ_LSMN0.4=0.0305S·cm^-1>σ_LSMS0.1=0.0182S·cm^-1>σ_LSM=0.00743S·cm^-1,doped W has the best conductivity.Compared with undoped W,the ionic conductivity has increased by 426%.The activation energy is Ea=1.702e V.According to the valence analysis,it may be that the doping amount is limited,and the low valence is not the main reason for improving the conductivity.On the other hand,from the ionic radius,the ionic radius of W is larger than that of Si,which is closer to Mo ion;Replacing Mo ions with W ions can achieve higher oxygen vacancy concentrations,lower activation energy,more favorable oxygen ion transport,larger oxygen ion conductor migration rate,and thus relatively higher ion conductivity.