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Doping effect on secondary phases, microstructure and electrical conductivities of LaGaO3 based perovskites
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
2009 (engelsk)Inngår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 29, nr 6, s. 1139-1146Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The intermediate temperature electrolytes La1-xSrxGa1-yMgyO3-delta (LSGM, where delta=(x+y)/2) with perovskite structure were prepared using a poly(vinyl alcohol) (PVA) solution polymerization method. Three secondary phases were identified by X-ray diffraction, LaSrGaO4, LaSrGa3O7 and La4Ga2O9. The relative amount of these secondary phases depended on the doping compositions. Sr doping produced more Sr rich secondary phases with increasing content, while enhanced solid solubility was observed with Mg addition. Sintered samples showed dense microstructures with well-developed equiaxed grains, and the secondary phases were mainly in the grain boundaries. LaSrGaO4 could not be detected by SEM for the sintered pellets. The oxygen ionic conductivity was enhanced by doping with Sr and Mg. Mg doping showed the increased conductivity activation energy. La0.8Sr0.2Ga0.9Mg0.1O2.85 had the highest ionic conductivity sigma = 0.128 S/cm at 800 degrees C in this work.

sted, utgiver, år, opplag, sider
2009. Vol. 29, nr 6, s. 1139-1146
Emneord [en]
Perovskite, Lanthanum gallate, Secondary phases, Microstructure, Ionic conductivity
HSV kategori
Identifikatorer
URN: urn:nbn:se:kth:diva-14237DOI: 10.1016/j.jeurceramsoc.2008.08.017ISI: 000264385000019Scopus ID: 2-s2.0-60649113400OAI: oai:DiVA.org:kth-14237DiVA, id: diva2:331844
Merknad
QC 20100727Tilgjengelig fra: 2010-07-27 Laget: 2010-07-27 Sist oppdatert: 2017-12-12bibliografisk kontrollert
Inngår i avhandling
1. Preparation and characterization of perovskite structure lanthanum gallate and lanthanum aluminate based oxides
Åpne denne publikasjonen i ny fane eller vindu >>Preparation and characterization of perovskite structure lanthanum gallate and lanthanum aluminate based oxides
2009 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

The present work was initiated to study the synthesis and properties of lanthanum gallate based oxides as intermediate temperature electrolyte for solid oxide fuel cells. The wet chemical method, polymer complexing route, was used to prepare the precursor powders. To further investigate the polymer complexing method, it was also applied to the preparation of lanthanum aluminate based oxides.

 

Single perovskite phase La0.8Sr0.2Ga0.83Mg0.17O2.815 can be prepared by the polymer complexing method using PVA as complexing agent. The thermal decomposition of the precursor powder undergoes three stages. While complete decomposition of the precursor is obtained at 1000°C. Further investigation of LaGaO3 doped with various amounts Sr or/and Mg was conducted. Three secondary phases were identified by X-ray diffraction, e.g. LaSrGaO4, LaSrGa3O7 and La4Ga2O9. The relative amount of these secondary phases depends on the doping compositions. Sr doping produced more Sr rich secondary phases with increasing content, while enhanced solid solubility was observed with Mg addition. Sintered samples showed dense microstructures with well-developed equiaxed grains, and the secondary phases were mainly in the grain boundaries. The oxygen ionic conductivity was enhanced by doping with Sr and Mg. Mg doping showed the increased activation energy of conductivity.

 

Preliminary study showed that the lanthanum gallate and ceria composite electrolyte is mainly fluorite CeO2 phase after sintering. The minority secondary phase, Sm3Ga5O12, was also detected by XRD. The composite electrolyte showed superior electrical performance. It exhibited the highest conductivity in the temperature range of 250–600°C, compared with lanthanum gallate and ceria specimens.

 

The phase pure perovskite La0.9Sr0.1Al0.85Mg0.1Co0.05O2.875 powders can easily be obtained by the polymer method using PVA as complexing agent. No secondary phase was detected after calcination at various temperatures (500–1100°C). The fully crystallized LaAlO3 phase was prepared after calcination at 900°C. Meanwhile the secondary phases were difficult to eliminate in the Sr- and Mg- doped LaGaO3 powder prepared by the same polymer method. It is thus concluded that the polymer, PVA in this work, provides more homogeneous mixing for cations of lanthanum aluminate based oxides, compared with the one for doped lanthanum gallate.

 

The influence of different complexing agents, e.g. PVA and PEG, was investigated in the synthesis of lanthanum aluminate powders. Minority impurity La2O3 existed in the PEG powder, but it could be eliminated after sintering at high temperatures. Although the pure phase LaAlO3 can be easily obtained in PVA powders calcined at 950°C, more seriously aggregated particles existed. PEG showed advantages over PVA in terms of better densification and microstructure control in the sintered products. To select proper polymers in complex oxide synthesis, the agglomeration and morphology of the powder are the most important factors to be considered.

 

sted, utgiver, år, opplag, sider
Stockholm: KTH, 2009. s. viii, 38
Emneord
Lanthanum gallate, lanthanum aluminate, ceria, composite, solid oxide fuel cell, electrolyte, polymer complexing.
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-10588 (URN)978-91-7415-324-8 (ISBN)
Disputas
2009-06-12, B2, Brinellvägen 23, KTH, Stockholm, 10:00 (engelsk)
Opponent
Veileder
Merknad
QC 20100727Tilgjengelig fra: 2009-06-04 Laget: 2009-05-29 Sist oppdatert: 2010-07-27bibliografisk kontrollert

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