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@INPROCEEDINGS{Alekseev:911410,
      author       = {Alekseev, Evgeny},
      title        = {{C}hemical and structural evolution of simple and complex
                      {T}h and {U} phases under high-pressure/high-temperature
                      conditions},
      reportid     = {FZJ-2022-04693},
      year         = {2022},
      abstract     = {Th and U are early actinides with fascinating and very
                      complex chemistry. Th is usually keeps 4+ oxidation state,
                      but uranium belongs to the most complex chemical elements
                      due to the owing 5f electrons. It is showing five oxidation
                      states and very diverse coordination environment in solid
                      state materials. Due to its extreme technological and
                      natural impact, uranium chemistry has been extensively
                      studied in last several decades. This talk will be focused
                      on U and Th inorganic phases that forms under extreme
                      conditions of HP (high pressure) and HT (high temperature).
                      The effects of pressure on structural formation of some Th
                      phases will be discussed. More complex is a behavior of
                      uranium under extreme condition because it is accomplished
                      with oxidation state change and formation of exotic
                      materials. For example formation of the stable
                      HP-modification of U2O5 which usually quite unstable under
                      normal conditions. The structure of HP-U2O5 is strongly
                      related to the fluorite–type UO2 (see Figure 1). That is
                      in strong contrast to the structure of the normal pressure
                      phase which is more related to the U(VI) phases. Using
                      crystallographic data for HP-U2O5 modification as a
                      reference, a DFT study of phase transition in pentavalent
                      uranium oxide has been made and delivered the accurate force
                      field parameters for U(V) in oxygen-bearing systems. In the
                      systems with U(VI), the so called uranyl groups (UO22+) are
                      forming. This group under normal conditions has a close to
                      linear O=U=O (178°) geometry. We found that pressure can
                      stabilize a strong bending of uranyl group within oxo-salt
                      phases. It is due to the creation of steric effects which
                      were not observed under normal conditions. For example, in
                      the HP- Na4[(UO2)(SO4)3], uranyl group is bended up to
                      165.6(12)°. DFT modelling confirmed that such configuration
                      is to be the most stable under high pressure.},
      month         = {Jun},
      date          = {2022-06-08},
      organization  = {Carnival Conference Session-2022,
                       Cologne (Germany), 8 Jun 2022 - 8 Jun
                       2022},
      subtyp        = {Invited},
      cin          = {IEK-9},
      cid          = {I:(DE-Juel1)IEK-9-20110218},
      pnm          = {1232 - Power-based Fuels and Chemicals (POF4-123)},
      pid          = {G:(DE-HGF)POF4-1232},
      typ          = {PUB:(DE-HGF)6},
      url          = {https://juser.fz-juelich.de/record/911410},
}