A Study of the Nonstoichiometry and Physical Properties of the Nd1-xBaxFeO3-y System

$Nd_{1-x}Ba_xFeO_{3-y}$계의 비화학량론과 물리적 성질에 관한 연구

  • 장순호 (연세대학교 이과대학 화학과) ;
  • 유광현 (연세대학교 이과대학 화학과) ;
  • 김성진 (이화여자대학교 화학과) ;
  • 최승철 (아주대학교 재료공학과) ;
  • 장순호 (한국전자통신연구원)
  • Published : 19940800

Abstract

A series of samples in the $Nd_{1-x}Ba_xFeO_{3-y}$ system has been prepared by heating the reactants to$1200^{\circ}C$ 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 $Fe^{3+}\;and\;Fe^{4+}$ ions, the nonstoichiometric chemical formulas could be determined from the mole ratio of $Fe^{4+}$ ion and oxygen vacacies. According to the Mossbauer spectroscopic analysis, the presence of 5-coordinated $FeO_5$ was evidenced only in the barium compounds along with $FeO_6,\;and\;FeO_4$, 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 $Fe^{3+}\;and\;Fe^{4+}$ ions. The electrical conductivities of all samples are within semiconducting range. Since the $Fe^{4+}$ ion acts as an electron acceptor level during the electron transfer between the Fe through intermediate $O^{2-}$ ions, the activation energy of the compounds decreases with the increment of $Fe^{4+}$ content.

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References

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