REPO4–BG composites synthesized by a new 1-step method were investigated and were found to be similar to the composite made by the traditional 2-step method.

Glass-ceramic composite materials are composed of ceramic crystallites within a glass matrix. These materials have been suggested as nuclear waste forms; however, the formation of targeted crystal phases remains a challenge to utilizing these materials as waste forms. The crystallization of composite materials consisting of CePO4 dispersed in borosilicate glass at low temperatures was investigated in this study. The basicity of the borosilicate glass matrix was decreased to favour Ce3+ and the formation of CePO4 at low annealing temperatures using a one-step coprecipitation method. The basicity of the glass was lowered by removing the network modifier oxides from the glass composition. The crystalline phases, Ce oxidation states, and elemental distribution in CePO4-Borosilicate Glass composite materials were studied by powder X-ray diffraction, Ce L1- and L3-edge X-ray absorption near-edge spectroscopy, and scanning electron microscopy/energy dispersive X-ray spectroscopy. Lowering the glass basicity was successful in favouring the formation of CePO4 and had the added benefit of reducing the crystallization of unwanted crystal phases.

Glass-ceramic composites are heterogeneous materials that have been suggested for use as nuclear waste form materials. A one-step coprecipitation method for synthesizing rare-earth phosphates (REPO4; RE = La or Ce) dispersed in a borosilicate glass (BG) matrix was investigated in this study. The effect of annealing temperature, ceramic loading, and oxidation state of the rare-earth precursor was explored using powder X-ray diffraction, scanning electron microscopy/energy dispersive X-ray spectroscopy, and X-ray absorption near-edge spectroscopy. REPO4 crystallites adopting the monazite structure were observed to form when the annealing temperature was 800–1100 °C in all REPO4–BG composite materials. Lowering the annealing temperature to 700 °C in the LaPO4–BG composite materials caused nm sized LaPO4 crystallites and crystalline SiO2 to form. No changes in the local chemical environment of La or P was observed as a result of the smaller LaPO4 crystallites. CeO2, crystalline SiO2, and Na3Ce­(PO4)2 formed in CePO4–BG composite materials in addition to CePO4 when the annealing temperature was below 1100 °C. CePO4 was not observed to form in CePO4–BG composite materials at low ceramic loadings and when annealed at 700 °C. CePO4 was found to be the favored crystal phase over CeO2 and Na3Ce­(PO4)2 in the CePO4–BG composite materials when the annealing temperature and ceramic loading was increased. The amount of CePO4 present was also found to be dependent on the oxidation state of the Ce precursor.

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