Localization model description of diffusion and structural relaxation in superionic crystalline UO₂.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Physical Chemistry

Background:

• Superionic conditions in crystalline UO2 involve significant anharmonic interactions.
• These interactions lead to non-Arrhenius relaxation and high ion mobility.
• Previous studies showed the Localization Model's utility in metallic glasses.

Purpose of the Study:

• To validate the Localization Model's prediction of a parameter-free relationship.
• To investigate the connection between alpha-structural relaxation time (τ_α), oxygen ion diffusion (D_O), and the Debye-Waller factor (⟨u²⟩).
• To assess the model's applicability under superionic conditions in UO2.

Main Methods:

• Simulations of crystalline UO2 under varying temperatures and pressures.
• Analysis of atomic dynamics, specifically picosecond-scale beta relaxation.
• Testing the predicted parameter-free relationship against simulation data.

Main Results:

• The Localization Model's predicted relationship holds to an excellent approximation.
• The parameter-free correlation between fast beta relaxation and long-time dynamics was confirmed.
• The findings are consistent across the investigated range of temperatures and pressures.

Conclusions:

• The Localization Model successfully describes the relationship between atomic dynamics and ion diffusion in UO2.
• The parameter-free nature of the LM relationship is robust, even under extreme conditions.
• This study validates the LM for predicting ion transport properties in complex materials.