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- The structural evolution and migration behaviour of strontium (Sr) in polycrystalline silicon carbide (SiC) co-implanted with helium (He) exceeding 300 °C were investigated at temperatures above 1000 °C. Sr ions were implanted into SiC at 600 °C (denoted as Sr-SiC-600) and co-implanted with He ions at 350 °C (denoted as Sr + He-SiC-600). Both samples were subsequently isochronally annealed at 1100 °C, 1200 °C, and 1300 °C for 5 h. Both as-implanted and annealed were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), and Rutherford backscattering spectrometry (RBS). Implantation at 600 °C resulted in a defective layer embedded in the crystalline SiC. Co-implantation led to the formation of He platelets in the defective layer, as well as blisters and large voids on the surface accompanied by slight migration of Sr. Annealing the Sr-SiC-600 samples up to 1300 °C resulted in formation of Sr precipitates accompanied by neither migration nor loss. Contrary annealing Sr + He-SiC-600 samples up to 1300 °C resulted in the formation of Sr precipitates accompanied by some loss of Sr. These results indicate trapping of Sr in both samples. This trapping was influenced by thermally activated cavities in the Sr-SiC-600 samples and by He induced cavities in the Sr + He-SiC-600 samples. These findings have significant implications for the design and performance of TRISO fuel particles.
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- MgAl2O4:x% Gd3+ (0 ≤ x ≤ 3) nano-powders were prepared via the citrate sol–gel method. The x-ray diffraction confirmed that the prepared samples consist of the cubic crystalline structures. There was no secondary phases due to Gd3+ doping. The estimated average grain sizes were found to be in the order of 8 nm. Energy dispersive spectroscopy showed the presence of the anticipated elements (Mg, Al, O, and Gd). The scanning electron microscope results revealed that the morphology of the samples is influenced by the Gd3+ concentration. Transmission electron microscopy analysis revealed that the prepared samples are in the nano-scale range. Selected area electron diffraction patterns indicated highly crystalline structure and the intensities of the bright spots varied with Gd3+ concentration. Photoluminescence studies showed two distinct emission peaks at 385 and 392 nm, which are certainly attributed to the defects levels located at different positions on the host material (MgAl2O4). The emission peaks located at 315 and 628 nm were respectively attributed to the 6P7/2 → 8S7/2 and 6G7/2 → 6P3/2 transitions in the Gd3+ ion. The luminescence intensity of the 388 nm decreased with an increase in the Gd3+ concentration. Commission Internationale de l’Eclairage (CIE) coordinates showed that the violet emission color from host cannot be tuned by varying Gd3+ concentration.
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