In situ high energy x-ray synchrotron diffraction study of the synthesis and stoichiometry of LaFeAsO and LaFeAsO1-xFy

TitleIn situ high energy x-ray synchrotron diffraction study of the synthesis and stoichiometry of LaFeAsO and LaFeAsO1-xFy
Publication TypeJournal Article
Year of Publication2009
AuthorsMcCallum RW, Yan JQ, Rustan GE, Mun ED, Singh Y, Das S, Nath R, Bud'ko SL, Dennis KW, Johnston DC, Canfield PC, Kramer MJ, Kreyssig A, Lograsso TA, Goldman AI
Journal TitleJournal of Applied Physics
Volume105
Pages123912
Date Published06/15
ISBN Number0021-8979
Accession NumberISI:000267599600093
Abstract

The reaction path for the synthesis of LaFeAsO and LaFeAsO1-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 degrees C <= T <= 1150 degrees C. Starting with LaAs, Fe2O3, Fe, and LaF3 as precursors, the results show that the synthesis is characterized by three temperature intervals: (1) Below 500 degrees C the sequential reduction of Fe2O3 and Fe3O4 takes place through the oxidization of LaAs. Below 400 degrees C, Fe2O3 is reduced to Fe3O4 by LaAs and then at 400 degrees C (T) 500 degrees C Fe3O4 is further reduced to Fe. (2) In the temperature interval 500 degrees C < T < 800 degrees 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 similar to 1040 degrees C. Possible reaction pathways and the difference between F-free and F-doped samples are discussed. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3149773]

URL<Go to ISI>://000267599600093
DOI10.1063/1.3149773