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KMID : 1059519940380080547
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Journal of the Korean Chemical Society
1994 Volume.38 No. 8 p.547 ~ p.551
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A Study of the Nonstoichiometry and Physical Properties of the Nd1-xBaxFeO3-y System
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Yo Chul-Hyun
Ryu Kwang-Hyun
Kim Sung-Jin
Choi Seung-Chul
Chang Soon-Ho
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Abstract
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A series of samples in the Nd1-xBaxFeO3-y system has been prepared by heating the reactants to1200℃ under an ambient atmosphere, and the solid solutions were identified by X-ray power diffraction analysis. The crystal systems of samples with x = 0.00 and 0.25 were found to be orthorhombic whose local symmetry is similiar to the distorted octahedral with orthoferrite type one, whereas those with x = 0.50 and 0.75 to be the cubic system. Since Fe ions in the solid solutions are a mixed valence state between Fe3+ and Fe4+ ions, the nonstoichiometric chemical formulas could be determined from the mole ratio of Fe4+ ion and oxygen vacacies. According to the Mossbauer spectroscopic analysis, the presence of 5-coordinated FeO5 was evidenced only in the barium compounds along with FeO6, and FeO4, but not in the strontium and calcium compounds. The samples with x = 0.25 and 0.50 show a spectrum of superparamagnetism, which might be due to the formation of a domain of the ferromagnetic interaction between the Fe3+ and Fe4+ ions. The electrical conductivities of all samples are within semiconducting range. Since the Fe4+ ion acts as an electron acceptor level during the electron transfer between the Fe through intermediate O2- ions, the activation energy of the compounds decreases with the increment of Fe4+ content.
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