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Thermochemical stability of BaFe12O19 and BaFe2O4 and phase relations in the Ba-Fe-O ternary system

Published online by Cambridge University Press:  03 March 2011

Jinshan Li
Affiliation:
Department of Materials Science and Engineering, Stanford University, Stanford, California 94305
Turgut M. Gür
Affiliation:
Center for Materials Research, Stanford University, Stanford, California 94305
Robert Sinclair
Affiliation:
Department of Materials Science and Engineering, Stanford University, Stanford, California 94305
Stephen S. Rosenblum
Affiliation:
Applied Electronics Center, Kobe Steel USA, Palo Alto, California 94304
Hidetaka Hayashi
Affiliation:
Applied Electronics Center, Kobe Steel USA, Palo Alto, California 94304
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Abstract

The stability of BaFe12O19 and BaFe2O4 was studied by the oxygen coulometric titration technique between 700 °C and 1000 °C using a solid-state electrochemical cell. This temperature range is technologically important for the deposition of BaFe2O19 magnetic thin films. The thermodynamic information obtained from the titration measurements was corroborated with structural identification of phases prepared under electrochemically controlled conditions. Accordingly, a section of the Ba–Fe–O ternary phase diagram around the BaFe12O19 composition was constructed in this temperature range. The standard Gibbs free energy change for the decomposition of BaFe12O19 into BaFe2O4, Fe3O4, and O2 is given by the expression Δ[J/mol] = 7.23 × 105 −480T. In the oxygen pressure-temperature domain, the thermodynamic stability limits of BaFe12O19 and BaFe2O4 are given by the expressions In[Po2(atm)] = 69.37 −1.04 × 105 T−1 and In[Po2(atm)] = 27.68 −7.12 × 104 T−1, respectively. The stability limits determined here help define the process conditions for the successful synthesis of these phases.

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Articles
Copyright
Copyright © Materials Research Society 1994

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