% IMPORTANT: The following is UTF-8 encoded.  This means that in the presence
% of non-ASCII characters, it will not work with BibTeX 0.99 or older.
% Instead, you should use an up-to-date BibTeX implementation like “bibtex8” or
% “biber”.

@PHDTHESIS{Hirschfeld:127760,
      author       = {Hirschfeld, Julian Arndt},
      title        = {{A}b initio investigation of ground-states and ionic motion
                      in particular inzirconia-based solid-oxide electrolytes},
      volume       = {187},
      school       = {Universität Duisburg-Essen},
      type         = {Dissertation},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2012-00715},
      isbn         = {978-3-89336-897-6},
      series       = {Schriften des Forschungszentrums Jülich Reihe Energie $\&$
                      Umwelt / Energy $\&$ Environment},
      pages        = {V, 144 S.},
      year         = {2013},
      note         = {Dissertation, Universität Duisburg-Essen, 2012},
      abstract     = {Electrolytes with high ionic conductivity at lower
                      temperatures are the prerequisite for the success of Solid
                      Oxide Fuel Cells (SOFC). One candidate is doped zirconia. In
                      thepast, the electrical resistance of zirconia based SOFC
                      electrolytes has mainly been decreased by reducing its
                      thickness. But there are limits to reducing the thickness
                      andone can say that nowadays the normal ways are basically
                      exhausted to further enhance the conductivity of well-known
                      electrolyte materials. Hence, new approaches need to be
                      found to discover windows of enhanced ionic conductivity.
                      This can be achieved by understanding the quantum-mechanical
                      oxygen transport in unconventional configurations of doped
                      zirconia. Therefore, such an understanding is of fundamental
                      importance. In this thesis two approaches are pursued, the
                      investigation of the strain dependent ionic migration in
                      zirconia based electrolytes and the designing of an
                      electrolyte material structure with enhanced and strongly
                      anisotropic ionic conductivity. The first approach expands
                      the elementary understanding of oxygen migration in oxide
                      lattices. The migration barrier of the oxygen ion jumps in
                      zirconia is determined by applying the Density Functional
                      Theory (DFT) calculations in connection with the Nudged
                      Elastic Band (NEB) method. These computations show an
                      unexpected window of decreased migration barriers at high
                      compressive strains. Similar to other publications a
                      decrease in the migration barrier for expansive strain is
                      observed. But, in addition, a migration barrier decrease
                      under high compressive strains is found beyond a maximal
                      height of the migration barrier. A simple analytic model
                      offers an explanation. The drop of the migration barrier at
                      high compressions originates from the elevation of the
                      ground-state energy. This means: Increasing ground state
                      energies becomes an interesting alternative to facilitate
                      ionic mobility. The second approach is based on the idea,
                      that actually, only in the direction of iontransport the
                      ionic conductivity in SOFC electrolytes is required to be
                      high. Using a layering of zirconium and yttrium in the
                      fluorite structure and applying DFT and NEBagain, a high
                      vacancy concentration and a very low migration barrier in
                      two dimensions is observed, while the mobility in the third
                      direction is sacrificed. The ionic conductivity of this new
                      structure at 500$^{\circ}$C surpasses that of the state of
                      the art electrolyte Yttrium Stabilized Zirconia (YSZ) at
                      800$^{\circ}$C. Throughout the process of searching for
                      augmented ionic conductivity, the NEB method has
                      particularly been used extensively and has been examined in
                      detail. This method has been applied to quite different
                      systems to gain a better understanding of it. While NEB has
                      been applied, it has been found that a certain modification
                      of the NEB, the Minimum search Nudged Elastic Band (MsNEB),
                      is able to find global minima in a complex phase space.
                      Furthermore, the MsNEB turns out to be complementary to
                      simulated annealing and the genetic algorithm. This new
                      scheme has not been applied to electrolyte materials, yet.
                      However, its capabilities have been demonstrated by
                      detectingthe most stable isomers of the phosphorus P$_{4}$,
                      P$_{8}$ molecules and the corresponding molecules of
                      A$_{s_n}$, Sb$_{n}$, Bi$_{n}$, (n = 4, 8). In the case of
                      P$_{8}$, the new MsNEB has led to a hitherto unknown
                      configuration, being more stable than the previously assumed
                      ground state.},
      keywords     = {Dissertation (GND)},
      cin          = {PGI-1 / IAS-1},
      cid          = {I:(DE-Juel1)PGI-1-20110106 / I:(DE-Juel1)IAS-1-20090406},
      pnm          = {424 - Exploratory materials and phenomena (POF2-424)},
      pid          = {G:(DE-HGF)POF2-424},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/127760},
}