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@ARTICLE{Sohn:190047,
      author       = {Sohn, Yoo Jung and Sparta, Karine M. and Prinz, Sebastian
                      and Meven, Martin and Roth, Georg and Heger, Gernot},
      title        = {{P}roton ordering in
                      ({NH}$_{4}$)$_{3}${H}({SO}$_{4}$)$_{2}$ at low-temperature
                      phase transitions},
      journal      = {Acta crystallographica / B},
      volume       = {69},
      number       = {4},
      issn         = {0108-7681},
      address      = {Oxford [u.a.]},
      publisher    = {Wiley-Blackwell},
      reportid     = {FZJ-2015-03006},
      pages        = {336-343},
      year         = {2013},
      abstract     = {Single-crystal neutron diffraction was used to investigate
                      the H-atom disorder in triammonium hydrogen disulfate
                      (TAHS), (NH4)3H(SO4)2, below room temperature. Crystal
                      structure analysis of the monoclinic phase III shows an
                      increase of proton ordering with decreasing temperature in
                      the (SO4)H(SO4) dimer. Moreover, the NH4(+) groups on a
                      general position begin ordering in this phase. The
                      monoclinic unit cell of TAHS-IV doubles in the b direction
                      and a slight distortion of SO4(2-) and NH4(+) tetrahedra is
                      observed. The order parameter introduced by Landau was
                      determined for the second-order II/III and III/IV phase
                      transitions from the intensities of the superstructure
                      reflections. TAHS-V has a triclinic space group and the
                      crystal structure seems to be completely ordered according
                      to a structure analysis by single-crystal X-ray diffraction
                      measurements. In addition, the decisive role of the
                      dynamical disorder of different ammonium groups on
                      successive phase transitions is discussed. Additional peaks
                      were observed by X-ray powder diffraction measurements at
                      ∼ 70 K on cooling, which refers to the V/VII phase
                      transition. These additional peaks remained up to
                      ∼ 85 K on heating. They were described with a doubling
                      of the unit cell along all three principal crystallographic
                      directions.},
      cin          = {JCNS (München) ; Jülich Centre for Neutron Science JCNS
                      (München) ; JCNS-FRM-II / JCNS-2 / IEK-1},
      ddc          = {530},
      cid          = {I:(DE-Juel1)JCNS-FRM-II-20110218 /
                      I:(DE-Juel1)JCNS-2-20110106 / I:(DE-Juel1)IEK-1-20101013},
      pnm          = {422 - Spin-based and quantum information (POF2-422) / 424 -
                      Exploratory materials and phenomena (POF2-424) / 542 -
                      Neutrons (POF2-542) / 544 - In-house Research with PNI
                      (POF2-544) / 54G - JCNS (POF2-54G24)},
      pid          = {G:(DE-HGF)POF2-422 / G:(DE-HGF)POF2-424 /
                      G:(DE-HGF)POF2-542 / G:(DE-HGF)POF2-544 /
                      G:(DE-HGF)POF2-54G24},
      experiment   = {EXP:(DE-MLZ)HEIDI-20140101},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000322373900004},
      doi          = {10.1107/S2052519213013092},
      url          = {https://juser.fz-juelich.de/record/190047},
}