Synthesis And Electrical Conductivity Of La_0.9Sr_0.1Ga_1-xM_xO_3-α Ceramics

High-temperature proton conductors have potential applications in some electrochemical devices and membrane reactors such as solid oxide fuel cells,hydrogen sensors,hydrogenation and dehydrogenation of some organic compounds,preparation by electrolyzing steam,separation and purification of hydrogen and ammonia synthesis at atmospheric pressure,etc.Ishihara discovered for the first time in 1994 that LaGaO₃ doped with Sr and Mg was a pure oxide-ionic conductor,which is considered as a promising candidate electrolyte for intermediate temperature fuel cell.However,the researches focused on its oxide-ionic conduction in the past decade.Recently,our group discovered for the first time that La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-αwas a superior proton conductor in hydrogen atmosphere.But there is no report on the proton conduction in LaGaO₃ doped with Sr²⁺and Zn²⁺.In addition,there are commonly some second-phases in the LaGaO₃ based ceramics synthesized by conventional solid-state reaction method.The La_0.9Sr_0.1Ga_1-xM_xO_3-α(M = Zn²⁺,Mg²⁺)ceramics were synthesized by solid-state reaction,sol-gel and microemulsion methods,and the ionic conduction properties of the ceramics were studied by various electrochemical methods including AC-impedance,Gas concentration cell,gas electrochemical permeation under various atmospheres at 600～1000℃.The main results in the present study are organized as the following:(1)La_0.9Sr_0.1Ga_1-xM_xO_3-αceramics were synthesized through three methods,and the orthorhombic perovskite single-phase was attained by the sol-gel and microemulsion methods,which solved the problem of impurity phases in LaGaO₃-based ceramics prepared by solid-state reaction.(2)La_0.9Sr_0.1Ga_1-xZn_xO_3-αceramics were discovered to have excellent protonic conduction under hydrogen atmosphere for the first time.It is a pure proton conductor with the proton transport number t_H⁺= 1 and proton conductivityσ_H⁺(at 700～1000℃)＞10^-2 S·cm^-1under hydrogen atmosphere.(3)It was found that it is a mixed ionic conductor(proton and oxide)under wet air atmosphere for the first time.(4)It was found that it is a pure oxide ionic conductor under dry oxygen atmosphere. (5)The differences in electrical properties between Sr²⁺- and Zn²⁺- doped LaGaO₃ and Sr²⁺- and Mg²⁺- doped LaGaO₃ were compared,and the mechanism responsible for the difference was discussed.