resumo
Ca2Fe1-xMnxAlO5 (0 <= x <= 1) compounds were prepared by a self-combustion method under air (x = 0, 0.1, 0.2 and 0.3) and nitrogen (x = 0.5, 0.7 and 1.0). The samples prepared under nitrogen were Successfully oxidized after short annealing under air. Both X-ray powder diffraction (XRD) Rietveld analysis and electron diffraction revealed that all compounds adopt the brownmillerite-type structure. All samples present an overall antiferromagnetic behaviour and data from magnetic measurements and Mossbauer spectroscopy allowed to Conclude that the transition temperature decreases as Mn content increases for x 0.3 and increases in the case of the x >= 0.5 Compounds. Except for x = 1, chemical disorder due to the Occupancy of both octahedral and tetrahedral sites by different metals as well as the competition between different moments' orientation induce a complex magnetic behaviour characterized by magnetic frustration and canted antiferromagnetism. Mossbauer spectroscopy and chemical titrations also allowed to conclude about the preferential oxidation of Mn3+ over Fe3+, obtained by thermal treatment under air of the x = 0.5 and 0.7 compositions. (C) 2008 Elsevier Inc. All rights reserved.
palavras-chave
LAYERED MANGANESE OXIDE; CRYSTAL-STRUCTURE; BROWNMILLERITE; CA2FEALO5; PEROVSKITES; SR2MNGAO5; CA2FE2O5; PHASE
categoria
Chemistry
autores
Carvalho, MD; Ferreira, P; Waerenborgh, JC; Tsipis, E; Lopes, AB; Godinho, M
nossos autores
Augusto Luís Barros Lopes
Professor Auxiliaragradecimentos
This work was supported by FCT, POCI, and co-financed by FEDER (POCI/QUI/58915/2004). E. Tsipis acknowledges FCT, Portugal, for the post-doctoral Grant SFRH/BPD/28629/2006.