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@PHDTHESIS{Sander:958368,
      author       = {Sander, Malte},
      othercontributors = {Roos, Christian Hans-Georg and Deubener, Joachim},
      title        = {{S}tructure and properties of thermally poled lithium
                      alumosilicate glasses and glass-ceramics},
      school       = {Rheinisch-Westfälische Technische Hochschule Aachen},
      type         = {Dissertation},
      address      = {Aachen},
      publisher    = {RWTH Aachen University},
      reportid     = {RWTH-2023-05238},
      pages        = {1 Online-Ressource : Illustrationen, Diagramme},
      year         = {2023},
      note         = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
                      University; Dissertation, Rheinisch-Westfälische Technische
                      Hochschule Aachen, 2023},
      abstract     = {A two-step process consisting of a thermal poling and a
                      crystallization treatment was developed to modify the
                      surface chemistry, structure, and properties of
                      glass-ceramics. A lithium alumosilicate glass was used to
                      study fundamental processes inside the glass throughout the
                      treatments. During the thermal poling treatment, a voltage
                      (50 to 1000 V) was applied to the glass at an elevated
                      temperature (200 to 500 °C), resulting in cation migration
                      toward the cathode. Underneath the anode-faced surface, the
                      depletion of lithium cations and an arising strong internal
                      electric field enabled electrons to discharge into the
                      anode. As a result, neutral non-bridging oxygens reacted
                      with each other, forming bridging oxygen and thus
                      polymerizing the network. ToF-SIMS element mappings and SNMS
                      depth profiles revealed an entire lithium depletion up to a
                      depth of 18.7 μm. Furthermore, Raman spectra of this region
                      pointed toward an increase in the extent of the mid-range
                      order and polymerization of the network. As a second charge
                      compensation mechanism, the formation of oxygen tri-clusters
                      was discussed based on atomic pair distribution functions.
                      The thermally poled glasses were subsequently crystallized.
                      During the treatment, thermally activated relaxation
                      processes enabled lithium cations to re-enter the depletion
                      layer. The relaxation processes were investigated by
                      measuring thermally stimulated depolarization currents
                      (TSDC). The TSDC measurements, in combination with thermal
                      analysis, revealed that the relaxation process was
                      interrupted by the high-quartz s.s. phase formation. During
                      the relaxation, only 25 $\%$ of the initial lithium cations
                      could re-enter the surface because sodium and potassium
                      occupied the interstitial charge-compensation sites in the
                      vicinity of non-bridging oxygen and charge deficit
                      tetrahedra. The lower lithium concentration underneath the
                      anode-faced surface limited the high-quartz s.s. phase
                      formation and caused the incorporation of a higher silica
                      content into the solid solution. Furthermore, grazing
                      incidence XRD revealed a characteristic bi-layered structure
                      underneath the anode-faced surface. Here, on top of the
                      surface, a low-crystalline layer was found that is followed
                      by an amorphous intermediate layer. SEM images and Raman
                      investigations showed that structural modifications
                      underneath the anode-faced surface of the glass-ceramics
                      extend deeper into the surface than the depletion layer in
                      the uncrystallized as-poled glasses. In layers beneath the
                      former depletion layer, high compressive stresses with
                      values up to −600 MPa were measured inside the crystalline
                      phase via RS-XRD. The stresses arise due to the layered
                      surface structure as well as different chemistry and thermal
                      expansion coefficients. Finally, a parameter study showed
                      that the depletion layer thickness is a state function of
                      the poling voltage as well as temperature and that its
                      chemical composition is identical in all poled samples.
                      Furthermore, it could be shown that the crystalline phase
                      content and silica content in the high-quartz s.s. phase is
                      only a function of the depletion layer thickness in the
                      as-poled glass.},
      cin          = {524210 / 520000},
      ddc          = {620},
      cid          = {$I:(DE-82)524210_20140620$ / $I:(DE-82)520000_20140620$},
      typ          = {PUB:(DE-HGF)11},
      doi          = {10.18154/RWTH-2023-05238},
      url          = {https://publications.rwth-aachen.de/record/958368},
}