Research On The Composition, Structure And Electrical Conductivity In Sr, Mg Doped LaGaO₃ Ceramics

Solid Oxide Fuel Cells (SOFC) is one of the most attractive energy conversion system because of its high efficiency, low pollution and fuel flexibility. However, the high operating temperature (>900 C) causes serious limitation in the choice of electrolyte materials. Lanthanum gallates doped with strontium on the A and magnesium on the B site, La1-xSrxGa1-yMgyO3-(X+y)/2 (LSGM100 100y), exhibit high electrical conductivity in lower temperature. It appears highly promising as a new solid oxide electrolyte for useing at medium temperature.Twenty seven kinds of the Strontium- and Magnesium-Doped LaGaO3 solid electrolytes with the perovskite structure were prepared by means of solid state reaction. The materials were characterized by room-temperature X-ray diffraction (XRD), scanning electron microscopy (SEM) and ac-impedance spectroscopy.Firstly, The region of the single-phase, cubic-perovskite, the two-phase ,cubic-perovskite and LaSrGaO4 or cubic-perovskite and LaSrGa3O7, and the three-phase, cubic- perovskite and LaSrGaO4 and LaSrGa3O7,shown in the region of the doped composition was determined from room-temperature XRD of the prepared materials.Secondly, the macro-structure taken by SEM show that the size of its grain increases with the sintering time. The electrical conductivity of LSGM increase with the size of its grain firstly ,.however, when the sintering time is longer than 24h, the electrical conductivity decrease with the size of its grain because of the second phase on the grain boundary.At last, the valence electron structure of ceramic phase in Strontium- and Magnesium-Doped LaGaO3 were calculated by EET theory, the results showed that the electrical conductivity is determined by the nA and the activation energy of the ceramic phase, we can forecast the ceramic optimizing composition with higher electrical conductivity by studying the nA and activation energy of the ceramic phase.