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@PHDTHESIS{Li:62607,
      author       = {Li, Haifeng},
      title        = {{S}ynthesis of {CMR} manganites and ordering phenomena in
                      complex transition metal oxides},
      volume       = {4},
      school       = {RWTH Aachen},
      type         = {Dr. (Univ.)},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {PreJuSER-62607},
      isbn         = {978-3-89336-527-2},
      series       = {Schriften des Forschungszentrums Jülich.
                      Schlüsseltechnologien / Key Technologies},
      pages        = {III, 175 S.},
      year         = {2008},
      note         = {Record converted from VDB: 12.11.2012; RWTH Aachen, Diss.,
                      2008},
      abstract     = {This dissertation covers: the instrumentation development;
                      the optimization synthesis of polycrystalline materials; the
                      single crystal growth of perovskite manganites; the
                      determination of crystal and magnetic structures from x-ray
                      and neutron powder diffraction data of polycrystalline and
                      powdered single-crystalline CMR La$_{1-x}$Sr$_{x}$MnO$_{3}$
                      manganites as well as its application in quantitatively
                      correlating structural and magnetic properties; the
                      application of resonant soft x-ray scattering in the
                      investigation of complex ordering phenomena in
                      La$_{7/8}$Sr$_{1/8}$MnO$_{3}$ and
                      La$_{1}$Sr$_{2}$Mn$_{2}$O$_{7}$ at the transition metal
                      L$_{II, III}$-edges and the rare earth M$_{IV, V}$-edges.
                      Two new devices have been developed: one is the rotating
                      specimen holder for laboratory x-ray powder diffraction,
                      which not only can effectively minimize the problem of
                      preferred orientation but also produces a
                      ‘zero-background’ contribution to the collected data;
                      another is the miniature goniometer for resonant soft x-ray
                      scattering, which makes it feasible to adjust samples along
                      $\chi$ (±2.5°) and $\Psi$ (360°) and dramatically
                      improves the efficiency of soft x-ray scattering chambers
                      and can be utilized to unravel the electronic ordering
                      phenomena by resonant soft x-ray scattering. The materials
                      synthesis is the first and critical step for any research in
                      condensed matter physics. One good route has been acquired
                      for preparing high-quality polycrystalline
                      La$_{7/8}$Sr$_{1/8}$MnO$_{3}$ samples, i.e. two times
                      calcining and two times sintering, through exploring various
                      preparation parameters. This synthesis route can be also
                      used to prepare high-quality La$_{1}$Sr$_{2}$Mn$_{2}$O$_{7}$
                      and La$_{0.83}$Ca$_{0.17}$MnO$_{3}$. Thus it is a universal
                      one for the present testing. The route for optimizing the
                      synthesis of polycrystalline manganites has been
                      established. One method for preparing straight and very
                      uniformly densified feed rods with a homogenous composition
                      distribution has been acquired, which makes growing large
                      high-quality single crystals possible. Three nominal
                      La$_{1-x}$Sr$_{x}$MnO$_{3}$ (x = 1/8) polycrystals prepared
                      under different conditions air, Ar and O$_{2}$ at 1 atm show
                      a huge contrast in the Curie temperature T$_{c}$. A combined
                      Rietveld refinement of the room-temperature x-ray and
                      neutron powder diffraction data has been performed for these
                      three samples. This study not only can determine the
                      relative content of the various elements (especially the
                      oxygen) with higher precision as compared to one probe
                      alone, but also makes it possible to correlate the drastic
                      change in Tc with the detailed structural parameters. In
                      addition, the individual effect of the number of nearest
                      magnetic neighbors on the structural and magnetic properties
                      has been investigated in detail using a set of
                      La$_{7/8}$Sr$_{1/8}$Mn$_{y}$O$_{3}$ samples with initial y =
                      0.97, 1.00 and 1.03. Moreover, a systematic neutron powder
                      diffraction study of the Ar annealed and air sintered
                      La$_{7/8}$Sr$_{1/8}$Mn$_{1- \gamma}$O$_{3+ \delta}$ samples
                      between 10 and 900 K has been performed, where the
                      structural and magnetic phases and their respective
                      transitions for two samples are completely different. For
                      the air sintered sample, a structural transition from
                      rhombohedral to orthorhombic upon cooling from 180 to 65 K
                      has been observed for the first time. From the refined
                      parameters the cooperative Jahn- Teller distortion parameter
                      $\Delta$, the tolerance factor $\textit{t}$ based on the
                      equilibrium La(Sr)-O and Mn-O bond lengths, and the
                      one-electron bandwidth $\textit{W}$ of the e$_{g}$-band have
                      been determined.},
      cin          = {IFF-4 / JARA-FIT / IFF-5 / Jülich Centre for Neutron
                      Science JCNS (JCNS) ; JCNS},
      cid          = {I:(DE-Juel1)VDB784 / $I:(DE-82)080009_20140620$ /
                      I:(DE-Juel1)VDB785 / I:(DE-Juel1)JCNS-20121112},
      pnm          = {Kondensierte Materie / Großgeräte für die Forschung mit
                      Photonen, Neutronen und Ionen (PNI)},
      pid          = {G:(DE-Juel1)FUEK414 / G:(DE-Juel1)FUEK415},
      typ          = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
      url          = {https://juser.fz-juelich.de/record/62607},
}