**3.3.2 Morphological study**

The SEM micrographs of the present series of compounds are shown in Fig. 11. All pictures were taken on sintered bars after they were prepared by the sol-gel and freeze-drying methods.

As observed, the Nd0.8Sr0.2(Mn1-xCox)O3 samples prepared by the sol-gel route show a homogeneous particle size morphology distributed in small agglomerates. The grain size of the nearly spherical particles decreases with Co content from ~ 200 nm for the sample with x = 0.1 to ~ 100 nm for x = 0.3. In the case of the compounds obtained by the freeze-drying technique the morphology of the particles is also spherical and homogeneous but the grain size is quite stable in all phases and slightly higher (~250 nm) than in the previous case.

According to some studies (Kuharuangrong et al., 2004), Co doping of 20% does not usually influence the grain size of LSM, but 40 % mol Co significantly reduces the grain size (about 5-10 m) of the La0.84Sr0.16Mn1-xCoxO3 (x= 0, 0.2, 0.4) samples prepared by conventional oxide mixing process. However, some reduction in the particle size was observed in the case of La0.67Pb0.33Mn1-xCoxO3 (x= 0 and 0.3) compounds, which were also prepared by the ceramic

Synthetic Methods for Perovskite Materials – Structure and Morphology 509

method always yields phases with higher particle sizes but this is not a disadvantage if the final compounds are not to be used in an application that requires high specific area. It is to note that in the case of the Nd0.8Sr0.2(Mn1-xCox)O3 , grain size was observed to change depending on the synthesis route. Although no significant differences were observed in the crystal structure, sol-gel method resulted in smaller grain sizes than the freeze drying method. In consequence, this seems to be a consequence of the preparative method which reinforces the idea that, if the microstructure of the sample is the key issue, the use of several

This work has been financially supported by the Ministerio de Ciencia e Innovación PSE-12000-2009-7 (MICINN) and MAT 2010-15375; Consejería de Industria, Innovación, Comercio y Turismo (SAIOTEK 2011) and by the Consejería de Educación, Universidades e Investigación (IT-177-07) of the Basque Goverment of Gobierno Vasco/Eusko Jaurlaritza. Technical and human support provided by SGIker (UPV/EHU, MICINN, GV, EJ, ESF) and Alternative Generation Systems Group of Technological Research Centre is gratefully

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**5. Acknowledgments** 

acknowledged.

**6. References** 

route (Dhahri et al., 2010). The present observation of a reduction in the particle size of the Nd0.8Sr0.2(Mn1-xCox)O3 phases in one of the methods but not in the other would point towards the synthesis method as the responsible for this effect, rather than the amount of cobalt. In this case, however, the observed decrease of the grain size is less significant than in previous studies.

Fig. 11. Secondary electron SEM micrographs obtained for all Nd0.8Sr0.2(Mn1-xCox)O3 compositions prepared by (a) sol-gel (sg) and (b) freeze-drying (fd) methods.
