Bulletin of the Korean Chemical Society

Korean Chemical Society (대한화학회)
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Study of the Nonstoichiometry and Physical Properties of the$Nd_{1-x}Sr_xFeO_{3-y}$ System

  • Published : 1994.08.20
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Abstract

The nonstoichiometric perovskite solid solutions of the $Nd_{1-x}Sr_xFeO_{3-y}$ system for the compositions of x=0.00, 0.25, 0.50, 0.75, and 1.00 have been prepared at $1150^{\circ}C$ in the air pressure. The compound of x=0.00, NdFe$O_{3.0}$, contains only $Fe^{3+}$ ion in octahedral site and the others involves the mixed valence state between $Fe^{3+}$ and $Fe^{4+}$ ions. The mole ratio of $Fe^{4+}$ ion or the ${\tau}$-value increases steadily with the x-value and then is maximized at the compositionof x= 1.00. The nonstoichiometric chemical formulas of the system are formulated from the x, ${\tau}$ and y values. From the Mossbauer spectroscopy, the isomer shift of $Fe^{3+}$ ion decreases with the increasing x-value, which is induced by the electron transfer between the$Fe^{3+}$ and $Fe^{4+}$ ions. The transfer is made possible by the indirect interaction between $Fe^{3+}$ and$Fe^{4+}$ ions via the oxygen ion. The eg electrons of the$Fe^{3+}$ ions are delocalized over all the Fe ions. Due to the electron transfer, the activation energy of electrical conductivity is decrease with the increasing amount of $Fe^{4+}$ ion.

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