Synthesis And Electrical Properties Research Of (La_1-xBa_x)₂(Mo_1-yNb_y)₂O_9-α As New Type Of Oxide-ion Conductors

La₂Mo₂O₉ is a new type of oxide ion conductor reported recently.There is highconcentration of oxygen vacancy in its sample even though without any other cationdoping.And La₂Mo₂O₉ exhibits high oxide ion conductivity than YSZ at 600～800℃.In this article a series of samples (La_1-xBa_x)₂Mo₂O_9-α(x= 1%,5%,10%,15%) wereprepared by a traditional high-temperature solid-state reaction method and characterizedwith XRD and SEM.The result showed that this series of samples were cubic structure.Using samples as solid electrolytes and porous platinum as electrodes,the ion conductionproperties of the samples were investigated by means of AC impedance spectroscopy,oxygen concentration cell and oxygen pump (electrochemical oxygen permeation) at 600～1000℃in various atmospheres.The observed values of oxygen concentration cell coincided with theoretical valuesperfectly,indicating that the oxide ion transference number is unity,which means thesamples were almost pure oxide-ion conductors in oxygen-containing atmospheres.Theelectrochemical oxygen permeation rate was in accordance with the theoretical ratecalculated from Faraday's law.This result confirmed that the samples were pure oxide ionconductors in oxygen-containing atmospheres.The oxide ionic conductivities of theceramic samples are higher than undoped La₂Mo₂O₉ and La_1.9Ba_0.1Mo₂O_9-αhas the highestoxide ionic conductivity with the value of 0.093 S·cm^-1(1000℃).We haven't found any report about the performances of La₂Mo₂O₉-based solid oxidefuel cell (SOFC) so far.The performances of SOFC based on (La_1-xBa_x)₂Mo₂O_9-α wereinvestigated in this study.The maximal outputs of current density and power density at1000℃reached 280mA·cm^-2 and 112mW·cm^-2 for the H₂-O₂ fuel cell,200 mA·cm^-2 and72mW·cm^-2 for the CH₄-O₂ fuel cell,respectively.The samples showed an electronicconduction to some extent under SOFC conditions.This may be resulted from the reduction of some Mo⁶⁺ in (La_1-xBa_x)₂Mo₂O_9-α to lower valence state in hydrogenatmosphere.The performance of CH₄-O₂ fuel cell was lower than that of H₂-O₂ fuel cell.This may be caused by the reformation of nature gas,which would consume some electricpower,resulting the reduction in the cell performance.Besides,we haven't found any report about double-doped La₂Mo₂O₉ ceramics withBa²⁺ on La³⁺ site and Nb⁵⁺ on Mo⁶⁺ site so far.The series of La_1.9Ba_0.1(Mo_1-yNb_y)₂O_9-α(y=4%,8%,12%) ceramics were synthesized by a high-temperature solid-state reactionmethod in this study,and the ion conduction properties were investigated by means ofsome electrochemical methods.The samples were almost pure oxide-ion conductors inhigh oxygen partial pressure atmospheres.Compared to the single-doped samples,the double-doped samples possess higheroxide ion conductivity due to the higher oxygen vacancy concentration in thedouble-doped samples.Among the double-doped samples,La_1.9Ba_0.1Mo_1.92Nb_0.08O_9-α hasthe highest oxide ion conductivity of 0.12S·cm^-1(1000℃).And the output power density ofH₂-O₂ fuel cell based on La_1.9Ba_0.1Mo_1.92Nb_0.08O_9-α is 133mW·cm^-2,which also superior tothe performance of fuel cell based on La_1.9Ba_0.1Mo₂O_9-α.