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Influence of A-site Nonstoichiometry on Microstructure and Electrical Properties of Lathanium Gallate Electrolyte Materials

Author: FanWeiYan
Tutor: ZhouDeFeng
School: Changchun University of
Course: Organic Chemistry
Keywords: Solid Electrolyte Electrical conductivity Nonstoichiometry Perovskite
CLC: TM911.4
Type: Master's thesis
Year: 2011
Downloads: 29
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Abstract


Classical LaGaO3 compound with a perovskite-structure is solid electrolyte materials in Solid Oxide Fuel Cells. Sr-and Mg-doped lathanium gallate has shown good and stable performance is a primary candidate to serve as the solid electrolyte in solid-oxide fuel cell. Its physical and chemical properties such as electrical conductivity, electronic structure, stability, and thermal expansion have been extensively studied. The doping of the perovskite LaGaO3 with Sr (in La-sites) and Mg (in Ga-sites) introduces a quantity of oxygen vacancies which results in high ionic conductivity. Moreover, these compositions have negligible electronic conductivity at temperatures lower than 1000℃within a broad range of oxygen partial pressure from 1 to-10-22 atm, and they have stable performance over long operating times. The transport properties of Lao.9Sro.1Gao.8Mgo.203-δ, are comparable to those of scandia-doped zirconia. And its conductivity is entirely ionic over wide oxygen partial pressure range, but is not as high as that of suitably doped ceria. The ionic conductivity of a material is attributed to this reason:various structure defects, for example, nonstoichimetry, because they introduce additional oxygen vacancies into the lattice, oxygen vacancies improve oxide ionic conductivity of material; In addition, nonstoichimetry can lead to the large distortion of the surrounding lattice, some extent suppresses the ordering processes in the oxygen sublattice. The nonstoichiometry in a given material may significantly affect its structure parameters and defect equilibrium, consequently changing matter and electrical transport characteristics especially for ionic conductive materials. This article we choose Lao.9Sro.1Gao.8Mgo.203-δ/ Lao.95Sro.o5Gao.9Mgo.i03-δsystem for this study, by changing A-site stoichiometry investigate the effect of A-site nonstoichiometry on the microstructure and electrical properties of the (Lao.9Sr0.1)xGao.8Mgo.203-δ/(Lao.95Sro.o5)xGao.9Mgo.i03-δ. In this paper:(1) (Lao.9Sro.1)xGao.8Mgo.2O3-δ(x= 0.97,1.00,1.03)were synthesized by citric-nitrate method, in 1400℃sintering. The characterization was carried out using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and electrical properties of the sintered samples were studied by A.C. impedance technology. The results showed that (Lao.9Sro.i)i.o3Gao.8Mgo.203-δsynthesized by citric-nitrate method have a good sinterability with high relative density (95.57%), at 450℃,σt= 10.45×10-4 S·cm-1, (Lao.9Sro.1)o.97Gao.8Mg0.203-δis relatively low density (94.70%), electrical performance is the worst (6.00X10-4 S·cm-1). And thus improved physical and electrical property was achieved in the sample with A-site excess non-stoichiometric. (2) (Lao.95Sro.o5)xGao.9Mgo.103-δ(x= 0.97,1.00,1.03)were synthesized by citric-nitrate method, in 1400℃sintering. The characterization was carried out using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and electrical properties of the sintered samples were studied by A.C. impedance technology. The results reveal that relative density(96.08%、96.58%) and electrical properties(σt= 7.18×10-4 S·cm-1,σt= 12.43×10-4 S·cm-1, at 500℃) of (La0.95Sr0.05)xGa0.9Mg0.1O3-δ(x= 0.97,1.03) ceramics are better than Lao.95Sr0.05Gao.9Mg0.1O3-δ(Relative Density= 95.70%,σt= 2.65×10-4 S·cm-1), and (Lao.95Sro.os)1.o3Gao.9Mgo.103-δis the best. Improved physical and electrical properties can be achieved in the sample with A-site nonstoichiometry.

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CLC: > Industrial Technology > Electrotechnical > Independent power supply technology (direct power) > Chemical power sources,batteries, fuel cells > Fuel cell
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