(A=Mg、Ca、Sr;B=Si)Preparation And Electrical Properties Of Co-doped Lanthanum Aluminate Based Electrolyte

Lanthanum aluminate,a new rare earth material,has been widely used in electronics,photocatalysis,high-temperature fuel cells,ceramic materials,sewage degradation catalysis,substrate growth materials and other fields.Compared with other perovskite materials,lanthanum aluminate system has more stable crystal structure and better mechanical properties.Perovskite-type lanthanum aluminate electrolyte and its doped derivative materials appear as new energy materials,which have the advantages of simple preparation process and cheap raw materials,and stand out among a number of electrolyte candidate materials for SOFCs（Solid Oxide Fuel Cell）.Si and Al belong to the same period,and their ion radii are similar,which satisfies the condition of doping radius ratio.In this paper,the element Si is selected for doping the Al site of LAO for the first time,and on this basis,the elements Mg,Sr and Ca are selected for co-doping it at the A site,so as to achieve the purpose of exploring SOFC electrolyte in a deeper level,provide technical reserves and support for its industrialization,and further contribute to the middle-low temperature and industrialization development of SOFCs.In this paper,the La Al_1-xSi_xO_3-δ（LASO）powder with fine particles and pure phase was synthesized by controlling the physical and chemical conditions of forming sol-gel and designing gel components,which can improve the electrochemical performance of ceramic blocks.On this basis,the positive influencing factors of doping were studied,and the elements were screened for co-doping,so as to find the best scheme of doping silicon at Al site and co-doping at La site at the same time,and finally an electrolyte material with good comprehensive properties was obtained,so as to maximize the material properties.After the doping experiment,Si doped La Al O₃solid electrolyte LASO material was successfully prepared.LASO is a ceramic sheet material obtained by sol-gel method,calcination at 800℃for 4 h,grinding,tabletting and sintering at 1100℃for 2 h.On this basis,more stable co-doped ceramic materialsLa_1-yMg_yAl_1-xSix O_3-δ（LMAS）,La_1-ySr_yAl_1-xSi_xO_3-δ（LSAS）,La_1-yCa_yAl_1-xSi_xO_3-δ（LCAS）were successfully prepared.XRD,FT-IR,SEM,EDS,Mapping,EIS and other characterization methods were used to detect the phase,surface microstructure and electrochemical properties of the sample.The results show that the LASO prepared by this method has good sintering activity,high crystallinity,uniform grain size,powder particle size of about 40 nm,lattice constant of 5.36（?）and no obvious distortion.Tests show that the conductivity can reach above 1.05*10^-4S/cm,the porosity reaches 3.8%and the conductance activation energy is not higher than 1.19 e V at 800℃.The co-doped systems all reached the maximum conductivity at 800℃,and the conductivity of LMAS was 4.11*10^-3S/cm when the content of Mg was x=0.15,and the conductivity activation energy was 1.31 e V;When the Sr doping content in LSAS system is x=0.30,the conductivity reaches 7.03*10^-3S/cm,which is dozens of times that of the parent phase LAO,and the conductivity activation energy is 1.27 e V;The conductivity of LCAS also reaches the maximum when the doping amount of Ca is x=0.30,which is 3.70*10^-4S/cm and the conductivity activation energy is 1.27 e V.In this paper,Si element is used to dope the B site of LAO,and the single doped sample LASO is successfully prepared,and the conductivity is not much different from that of the parent phase LAO.At the same time,the co-doping of Mg,Sr and Ca at La site was tried on the basis of LASO sample,and the electrochemical performance of LSAS system was the best,and the conductivity was increased by 70times when the activation energy was only increased by 12.4%.This paper can provide some precursor work for metalloid doping and co-doping of perovskite in the future.