In situ high energy x-ray synchrotron diffraction study of the synthesis and stoichiometry of LaFeAsO and LaFeAs O1-xFy

R. W. McCallum, J. Q. Yan, G. E. Rustan, E. D. Mun, Yogesh Singh, S. Das, R. Nath, S. L. Bud'Ko, K. W. Dennis, D. C. Johnston, P. C. Canfield, M. J. Kramer, A. Kreyssig, T. A. Lograsso, A. I. Goldman

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Abstract

The reaction path for the synthesis of LaFeAsO and LaFeAsO 1-xFy by solid state reaction was studied by in situ high temperature x-ray diffraction technique and differential thermal analysis in the temperature interval 100 °C≤T≤1150 °C. Starting with LaAs, Fe2O3, Fe, and La F3 as precursors, the results show that the synthesis is characterized by three temperature intervals: (1) Below 500 °C the sequential reduction of Fe2O3 and Fe3O4 takes place through the oxidization of LaAs. Below 400 °C, Fe2O3 is reduced to Fe3O 4 by LaAs and then at 400 °C<T<500 °C Fe 3O4 is further reduced to Fe. (2) In the temperature interval 500 °C<T<800 °C, multiple intermediate reactions take place resulting in the formation of FeAs and La2O3. (3) The formation of LaFeAsO based phase could be unambiguously resolved above 800 °C. For both LaFeAsO and LaFeAsO1-xFy, FeAs is a primary impurity at high temperatures that melts at ∼1040 °C. Possible reaction pathways and the difference between F-free and F-doped samples are discussed.

Original languageEnglish
Article number123912
JournalJournal of Applied Physics
Volume105
Issue number12
DOIs
StatePublished - 2009
Externally publishedYes

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