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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},
}