Investigation of Radiation Damage in the Monazite-Type Solid Solution La_1-CePO₄

Area of Science:

• Materials Science
• Nuclear Engineering
• Solid-State Chemistry

Background:

• Monazite ceramics are promising for immobilizing radionuclides due to their inherent radiation stability.
• Understanding the response of monazite solid solutions to radiation damage is crucial for nuclear waste management applications.

Purpose of the Study:

• To investigate the role of structural chemistry in the irradiation stability of La_1-xCe_xPO₄ (x = 0.25, 0.5, 0.75, 1) solid solutions.
• To assess the suitability of these monazite ceramics for long-term radionuclide immobilization under irradiation.

Main Methods:

• High-resolution structural studies using scanning electron microscopy (SEM), Raman spectroscopy, grazing incidence X-ray diffraction (GI-XRD), and HERFD-EXAFS.
• Irradiation of ceramic samples with 14 MeV Au ions at fluences of 10¹⁴ and 10¹⁵ ions/cm² to simulate nuclear recoil events.

Main Results:

• SEM and Raman spectroscopy indicated significant structural damage, with grain boundaries acting to impede defect propagation.
• GI-XRD revealed that monazite maintains crystallinity at high fluences, showing both amorphization and recrystallization.
• Atomic disorder increased post-irradiation, but short-range order was largely preserved, facilitating recrystallization, though compositionally dependent.

Conclusions:

• Monazite solid solutions exhibit notable radiation damage resistance, retaining crystallinity and short-range order.
• Compositions with uneven cation ratios (La_0.75Ce_0.25PO₄ and La_0.25Ce_0.75PO₄) showed reduced radiation damage resistance.
• The study provides insights into monazite solid solution chemistry relevant to radionuclide immobilization strategies.