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@ARTICLE{Rodenbcher:1014684,
      author       = {Rodenbücher, Christian and Bihlmayer, Gustav and Korte,
                      Carsten and Rytz, Daniel and Szade, Jacek and Szot, Kristof},
      title        = {{A}n {O}perando {S}tudy of the {T}hermal {R}eduction of
                      {B}a{T}i{O}3 {C}rystals: {T}he {N}ature of the
                      {I}nsulator–{M}etal {T}ransition of the {S}urface {L}ayer},
      journal      = {Crystals},
      volume       = {13},
      number       = {8},
      issn         = {2073-4352},
      address      = {Basel},
      publisher    = {MDPI},
      reportid     = {FZJ-2023-03389},
      pages        = {1278 -},
      year         = {2023},
      abstract     = {The insulator-to-metal transition upon the thermal
                      reduction of perovskites is a well-known yet not completely
                      understood phenomenon. By combining different
                      surface-sensitive analysis techniques, we analyze the
                      electronic transport properties, electronic structure, and
                      chemical composition during the annealing and cooling of
                      high-quality BaTiO3 single crystals under ultra-high-vacuum
                      conditions. Our results reveal that dislocations in the
                      surface layer of the crystal play a decisive role as they
                      serve as easy reduction sites. In this way, conducting
                      filaments evolve and allow for turning a macroscopic crystal
                      into a state of metallic conductivity upon reduction,
                      although only an extremely small amount of oxygen is
                      released. After annealing at high temperatures, a valence
                      change of the Ti ions in the surface layer occurs, which
                      becomes pronounced upon the quenching of the crystal. This
                      shows that the reduction-induced insulator-to-metal
                      transition is a highly dynamic non-equilibrium process in
                      which resegregation effects in the surface layer take place.
                      Upon cooling to the ferroelectric phase, the metallicity can
                      be preserved, creating a “ferroelectric metal.” Through
                      a nanoscale analysis of the local conductivity and
                      piezoelectricity, we submit that this phenomenon is not a
                      bulk effect but originates from the simultaneous existence
                      of dislocation-based metallic filaments and
                      piezoelectrically active areas, which are spatially
                      separated.},
      cin          = {IEK-14 / PGI-1},
      ddc          = {540},
      cid          = {I:(DE-Juel1)IEK-14-20191129 / I:(DE-Juel1)PGI-1-20110106},
      pnm          = {5211 - Topological Matter (POF4-521) / 1231 -
                      Electrochemistry for Hydrogen (POF4-123)},
      pid          = {G:(DE-HGF)POF4-5211 / G:(DE-HGF)POF4-1231},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:001055257000001},
      doi          = {10.3390/cryst13081278},
      url          = {https://juser.fz-juelich.de/record/1014684},
}