Journal of Alloys and Compounds 480 (2009) 279–285 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Effect of the synthesis route on the microstructure and the reducibility of LaCoO 3 S. Ivanova a , A. Senyshyn b , E. Zhecheva a , K. Tenchev c , V. Nikolov a , R. Stoyanova a,∗ , H. Fuess b a Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria b Darmstadt University of Technology, Institute of Materials Science, Structure Research, Petersenstr. 23, D-64287 Darmstadt, Germany c Institute of Catalysis, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria article info Article history: Received 10 December 2008 Received in revised form 17 February 2009 Accepted 21 February 2009 Available online 5 March 2009 Keywords: Oxide materials Sol–gel processes Reduction X-ray diffraction SEM Electron paramagnetic resonance abstract The effect of the synthesis route on the microstructure and reducibility of lanthanum cobaltates (LaCoO 3 ) perovskites was examined. Two synthesis methods were used: thermal decomposition of freeze-dried La–Co-citrates and the Pechini method. The crystal structure, morphology and defect structure of LaCoO 3 were characterized by XRD powder diffraction, TEM and SEM analyses and electron paramagnetic reso- nance spectroscopy. The reducibility was tested by thermal programmed reduction with hydrogen. The intermediate stage of reduction was determined by ex situ XRD experiments. LaCoO 3 powders obtained by the Pechini method were reduced relatively easier as LaCoO 3 obtained from freeze-dried citrates. The LaCoO 3 reduction yielded Co metal and La 2 O 3 via the formation of oxygen deficient Brownmillerite-type La 3 Co 3 O 8 and La 2 Co 2 O 5 oxides. For LaCoO 3 obtained from freeze-dried citrates and annealed at higher temperatures, Co metal, in addition to oxygen deficient perovskites, was formed at the initial stage of the reduction. The different reducibility of LaCoO 3 obtained by the Pechini method and that from the freeze-dried citrates was discussed taking into account the formation of oxygen-deficient phases from the Brownmillerite and Ruddlesden–Popper series during the reduction. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Lanthanum cobaltates (LaCoO 3 ) with a perovskite type structure are recognized as promising cathode materials for intermediate- temperature solid oxide fuel cells, as well as automotive exhaust catalysts [1–3]. The state-of-the-art research is mainly devoted to the improvement of the performance of LaCoO 3 by development of rational methods of synthesis that influences the morphology and microstructure. Among several synthesis procedures including solution-based and solid-state reactions [4–19], the most widely used method is the Pechini method [20]. This method is based on the mixing of La and Co ions at an atomic scale by the use of citric acid as a chelating agent and of ethylene glycol to form a polyester- type resin [8,9,21–23]. One of the factors determining the LaCoO 3 application is the mobility of lattice oxygen [24–26]. To evaluate this factor, temperature-programmed reduction with H 2 is often used as a fast screening method [24,25]. The reduction of LaCoO 3 has been con- troversially discussed. Some authors [27–29] propose a two step process via intermediate oxygen-deficient oxides before the final reduction to Co metal and La 2 O 3 . Other reports [30–33], however, suggest one-step reduction directly to Co metal based on XRD, IR ∗ Corresponding author. Tel.: +359 2 9793915; fax: +359 2 8705024. E-mail address: radstoy@svr.igic.bas.bg (R. Stoyanova). and XPS evidence. Irrespective of the intensive studies on the mech- anism of LaCoO 3 reduction, the relationship between the synthesis procedure and reducibility of LaCoO 3 has only been studied sporad- ically [34]. The examination of this relationship is further initiated by the fact that the synthesis procedure affects the microstructure of LaCoO 3 [35–39]. The present study is aimed at examining the effect of the syn- thesis route on the microstructure and reducibility of LaCoO 3 . Two solution-based methods were used for the preparation of LaCoO 3 . The first one is the Pechini method. The second one is based on the formation of mixed La–Co-citrate precursors by freeze-drying of the corresponding solutions. To analyse the effect of the organic com- ponent on the morphology of LaCoO 3 , the same metal-to-citric acid ratio (La:Co:citric acid = 1:1:10) was used for both methods. Ther- mal properties of freeze-dried citrates and Pechini-type precursors were followed by DTA and TG analysis. Structural and morphologi- cal characterization was made by XRD powder diffraction, TEM and SEM analysis. Electron paramagnetic resonance (EPR) spectroscopy was used to analyze the defect structure of LaCoO 3 . The reducibility was tested by thermal programmed reduction (TPR) with hydrogen. The intermediate study of reduction was determined by ex situ XRD experiments. 2. Experimental Homogeneous La–Co-citrate precursors were obtained by freeze-drying and by a Pechini-type reaction. Lanthanum–cobalt citrates were prepared by adding a 5M 0925-8388/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2009.02.096