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@ARTICLE{Mittal:14216,
      author       = {Mittal, R. and Mishra, S. K. and Chaplot, S. L. and
                      Ovsyannikov, S. V. and Greenberg, E. and Trots, D. M. and
                      Dubrovinsky, L. and Su, Y. and Brückel, T. and Matsuishi,
                      S. and Hosono, H. and Garbarino, G.},
      title        = {{A}mbient- and low-temperature synchrotron x-ray
                      diffraction study of {B}a{F}e2{A}s2 and {C}a{F}e2{A}s2 at
                      high pressures up to 56 {GP}a},
      journal      = {Physical review / B},
      volume       = {83},
      number       = {5},
      issn         = {1098-0121},
      address      = {College Park, Md.},
      publisher    = {APS},
      reportid     = {PreJuSER-14216},
      pages        = {054503},
      year         = {2011},
      note         = {R.M. and S.K.M. thank the Department of Science and
                      Technology (DST), India for providing financial support to
                      carry out synchrotron x-ray diffraction at European
                      Synchrotron Radiation Facility, Grenoble, France. We thank
                      M. Hanfland and W. Crichton for loading the helium into the
                      cells for our measurements carried out at ESRF.},
      abstract     = {We report on high-pressure powder synchrotron x-ray
                      diffraction studies on MFe2As2 (M = Ba, Ca) over a range of
                      temperatures and pressures up to about 56 GPa using a
                      membrane diamond-anvil cell. Our data indicate a phase
                      transition to a collapsed tetragonal phase in both compounds
                      upon compression. The data at 300 K are measured in both
                      pressure-increasing and -decreasing cycles. Our measurements
                      show that at 300 K in the Ba compound, the transition occurs
                      at 27 GPa, which is much higher than the transition pressure
                      of 1.7 GPa in the Ca compound. At low temperature, we could
                      obtain data only in the pressure-increasing cycle, therefore
                      a precise transition pressure is not identified. At a low
                      temperature of 33 K, the transition to the tetragonal phase
                      in the Ba compound starts, upon compression, at about 29
                      GPa, which is much higher than the transition pressure of
                      0.3 GPa at 40 K as known in the case of the Ca compound. The
                      much higher transition pressure in the Ba compound may be
                      due to its larger unit-cell volume at ambient pressure. It
                      is important to note that the transition in both compounds
                      occurs when they are compressed to almost the same value of
                      the unit-cell volume and attain similar c(t)/a(t) ratios. We
                      also show that the FeAs4 tetrahedra are much less
                      compressible and more distorted in the collapsed tetragonal
                      phase than their nearly regular shape in the ambient
                      pressure phase. We present a detailed analysis of the
                      pressure dependence of the structures as well as equations
                      of state in these important BaFe2As2 and CaFe2As2
                      compounds.},
      keywords     = {J (WoSType)},
      cin          = {PGI-4 / JCNS-1 / Jülich Centre for Neutron Science JCNS
                      (JCNS) ; JCNS / JARA-FIT / JCNS-2},
      ddc          = {530},
      cid          = {I:(DE-Juel1)PGI-4-20110106 / I:(DE-Juel1)JCNS-1-20110106 /
                      I:(DE-Juel1)JCNS-20121112 / $I:(DE-82)080009_20140620$ /
                      I:(DE-Juel1)JCNS-2-20110106},
      pnm          = {Großgeräte für die Forschung mit Photonen, Neutronen und
                      Ionen (PNI) / Grundlagen für zukünftige
                      Informationstechnologien},
      pid          = {G:(DE-Juel1)FUEK415 / G:(DE-Juel1)FUEK412},
      shelfmark    = {Physics, Condensed Matter},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000287129700008},
      doi          = {10.1103/PhysRevB.83.054503},
      url          = {https://juser.fz-juelich.de/record/14216},
}