TY  - CONF
AU  - Alekseev, Evgeny
TI  - Chemical and structural evolution of simple and complex Th and U phases under high-pressure/high-temperature conditions
M1  - FZJ-2022-04693
PY  - 2022
AB  - 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.
T2  - Carnival Conference Session-2022
CY  - 8 Jun 2022 - 8 Jun 2022, Cologne (Germany)
Y2  - 8 Jun 2022 - 8 Jun 2022
M2  - Cologne, Germany
LB  - PUB:(DE-HGF)6
UR  - https://juser.fz-juelich.de/record/911410
ER  -