Pressure dependence of the low- temperature crystal structure and phase transition behaviour of CaFeAsF and SrFeAsF: A synchrotron x-ray diffraction study
| Autor: | Mishra, S. K., Mittal, R., Chaplot, S. L., Ovsyannikov, S. V., Trots, D. M., Dubrovinsky, L., Su, Y., Brueckel, Th., Matsuishi, S., Hosono, H., Garbarino, G. |
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| Rok vydání: | 2011 |
| Předmět: | |
| Zdroj: | Physical Review B 84, 224513 (2011) |
| Druh dokumentu: | Working Paper |
| DOI: | 10.1103/PhysRevB.84.224513 |
| Popis: | We report systematic investigation of high pressure crystal structures and structural phase transition upto 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 Pc = 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 & 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 upto 25 GPa at 300 K. The dPc/dT is found to be positive for the CaFeAsF & CaFe2As2, however the same was not found in case of BaFe2As2. We discuss observations of structural evolution in the context of superconductivity in these and other Fe-based compounds. It appears that the closeness of the Fe-As-Fe bond angle to its ideal tetrahedral value of 109.470 might be associated with occurrence of superconductivity at low temperature. Comment: 23 pages, 11 Figures |
| Databáze: | arXiv |
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