Journal Article

PreJuSER-20184

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Pressure dependence of the low-temperature crystal structure and phase transition behavior of CaFeAsF and SrFeAsF: A synchrotron x-ray diffraction study

Mishra, S. K. ; Mittal, R. ; Chaplot, S. L. ; Ovsyannikov, S. V. ; Trots, D. M. ; Dubrovinsky, L. ; Su, Y.FZJ* ; Brückel, T.FZJ* ; Matsuishi, S. ; Hosono, H. ; Garbarino, G.

2011
APS College Park, Md.

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Please use a persistent id in citations: http://hdl.handle.net/2128/10871  doi:10.1103/PhysRevB.84.224513

Abstract: We report systematic investigation of high pressure crystal structures and structural phase transition up to 46 GPa in CaFeAsF and 40 GPa in SrFeAsF at 40 K using powder synchrotron x-ray diffraction experiments and Rietveld analysis of the diffraction data. We find that CaFeAsF undergoes orthorhombic to monoclinic phase transition at P-c = 13.7 GPa while increasing pressure. SrFeAsF exhibits coexistence of orthorhombic and monoclinic phases over a large pressure range from 9 to 39 GPa. The coexistence of the two phases indicates that the transition is of first order in nature. Unlike in the 122 compounds (BaFe2As2 and CaFe2As2), we do not find any collapse tetragonal transition. The transition to a lower symmetry phase (orthorhombic to monoclinic) in 1111 compounds under pressure is in contrast with the transition to a high symmetry phase (orthorhombic to tetragonal) in 122-type compounds. On heating from 40 K at high pressure, CaFeAsF undergoes monoclinic to tetragonal phase transition around 25 GPa and 200 K. Further, it does not show any post-tetragonal phase transition and remains in the tetragonal phase up to 25 GPa at 300 K. The dP(c)/dT is found to be positive for the CaFeAsF and CaFe2As2, however the same was not found in case of BaFe2As2.

Keyword(s): Basic research (1st) ; Others (1st) ; Crystallography (2nd) ; J

Note: R. Mittal and S. K. Mishra thank the Department of Science and Technology (DST), India for providing financial support to carry out synchrotron x-ray diffraction at the European Synchrotron Radiation Facility, Grenoble, France.

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Contributing Institute(s):

1. Streumethoden (PGI-4)
2. Jülich-Aachen Research Alliance - Fundamentals of Future Information Technology (JARA-FIT)
3. JCNS-FRM-II (JCNS (München) ; Jülich Centre for Neutron Science JCNS (München) ; JCNS-FRM-II)
4. Streumethoden (JCNS-2)

Research Program(s):

1. Grundlagen für zukünftige Informationstechnologien (P42)
2. Großgeräte für die Forschung mit Photonen, Neutronen und Ionen (PNI) (P55)

Experiment(s):

1. No specific instrument

Appears in the scientific report 2011

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