Structure-thermodynamics relationship of schoepite from first-principles

Area of Science:

• Materials Science
• Geochemistry
• Computational Chemistry

Background:

• Schoepite, a uranyl phase [(UO2)8O2(OH)12]·12H2O, forms during UO2 corrosion.
• Understanding its structure-thermodynamic properties is crucial for nuclear waste management and geochemistry.

Purpose of the Study:

• Investigate the relationship between schoepite's structure and its thermodynamic properties.
• Utilize density functional perturbation theory (DFPT) for accurate predictions.

Main Methods:

• Employed density functional theory (DFT) to reproduce experimental crystallographic lattice parameters.
• Performed phonon calculations using the quasi-harmonic approximation.
• Calculated standard molar entropy (S0) and isobaric heat capacity (C0P).

Main Results:

• DFT accurately reproduced experimental lattice parameters.
• Predicted S0 = 179.60 J mol-1 K-1 and C0P = 157.4 J mol-1 K-1 at 298.15 K.
• Showed a nearly linear variation of heat capacity with water content across a temperature range of 100–500 K.

Conclusions:

• DFPT provides reliable predictions for schoepite's thermodynamic behavior.
• Findings offer critical data for modeling uranyl phase dehydration and the behavior of hygroscopic materials.