DFT and two-dimensional correlation analysis methods for evaluating the Pu³⁺–Pu⁴⁺ electronic transition of plutonium-doped zircon

Highlights: • Effect of Pu f-shell electron on the electronic property of zircon is calculated via DFT and 2D-CA techniques. • Reasons of Pu f-shell electron influencing on electronic properties are systematically discussed. • Phase transitions are found at two point 2.8 mol% and 7.5 mol%. - Abstract: Understanding how plutonium (Pu) doping affects the crystalline zircon structure is very important for risk management. However, so far, there have been only a very limited number of reports of the quantitative simulation of the effects of the Pu charge and concentration on the phase transition. In this study, we used density functional theory (DFT), virtual crystal approximation (VCA), and two-dimensional correlation analysis (2D-CA) techniques to calculate the origins of the structural and electronic transitions of Zr_1−cPu_cSiO₄ over a wide range of Pu doping concentrations (c = 0–10 mol%). The calculations indicated that the low-angular-momentum Pu-f_xy-shell electron excites an inner-shell O-2s² orbital to create an oxygen defect (V_O-s) below c = 2.8 mol%. This oxygen defect then captures a low-angular-momentum Zr-5p⁶5s² electron to form an sp hybrid orbital, which exhibits a stable phase structure. When c > 2.8 mol%, each accumulated V_O-p defect captures a high-angular-momentum Zr-4d_z electron and two Si-p_z electrons to create delocalized Si⁴⁺ → Si²⁺ charge disproportionation. Therefore, we suggest that the optimal amount of Pu cannot exceed 7.5 mol% because of the formation of a mixture of ZrO₈ polyhedral and SiO₄ tetrahedral phases with the orientation (10-1). This study offers new perspective on the development of highly stable zircon-based solid solution materials