The Defect Analysis And Application Of Neutron Irradiated6H-SiC

Silicon carbide (SiC) is a superior irradiation-resistance material. It can be usedfor fabricating the irradiation resistance electronic devices and irradiation detectors.The SiC-based ceramics and composites are the potential materials for the fusionplasma-facing components. During the application in severe irradiation environment,the irradiation induced defects will lead directly to the deterioration of performances.It is essential to recognize the formation mechanism and microstructure of irradiationdefects and the effect of defects on the macroscopic properties. The confocalmicro-Raman spectroscopy and X-ray diffraction were employed to investigate the6H-SiC neutron irradiated up to1.72×1019and1.67×1020n/cm2. The details are asfollows:1. The Si-Si related peaks at189,275,437, and539cm-1, the Si-C related peaksat610,657, and712cm-1, and C-C related peak at1420cm-1are recorded. Afterhigh-fluence neutron irradiation, the peaks at1357and1603cm-1are also measured.They agree well with A1gand E2gin disordered graphite. These scattering peaksindicate that irradiation leads to the production of Si clusters, sp2/sp3C clusters andgraphite clusters.2. Irradiation results in the appearance of the low-frequency tails of the FTO2/6and FLO0/6optical peaks, which is phonon confinement effect. Irradiation defects alsodiminish unequally the frequency of the FTO2/6and FLO0/6peaks, leading to thereduction of FLO0/6-FTO2/6splitting. The annealing evolution demonstrates that theVCand VSiare responsible mainly for the reduction of the FLO0/6-FTO2/6splitting.3. Annealing experiments reflect that the Si clusters, sp2/sp3C clusters andgraphite clusters are removed after1100,1000and800oC annealing treatments,respectively. In addition, an interesting peak at575cm-1is measured during annealingtreatment. It emerges initially after annealing at800oC and vanishes at1400oC. Thisevolution indicates the575cm-1originates from the Si-C vibration of CSiVCcomplex.4. The formation of graphite clusters depends strongly on the neutron fluenceand intentionally incorporated N impurity. Essentially, the formation originates fromN aggregation but not from NCdonor. During neutron irradiation, N aggregation cantransform into CSi(NC)2complex, which contains the sp2C=C pair. The sp2C=C paircan act as the graphite nucleus.5. Pre-irradiation annealing treatment can decrease the concentration of graphite clusters. After the pre-irradiation annealing treatment at1000oC, the graphite clustersbecome almost undetectable because the N aggregation dissociates into isolated Natoms and then there is no pproduction of sp2C=C pair in SiC during the subsequentirradiation.6. The X-ray diffraction measurement and transmission electron microscopyanalysis indicate that there are mainly points, clusters, and amorphous regions in thesamples neutron irradiated up to the two fluences.7. The X-ray diffraction was employed to analyze the annealing recovery of theFWHM (full with at the half maximum) of the (006) diffraction peak, which showsthe200-800oC,800-1400oC, and1400-1600oC recovery stages.8. Based on the above mentioned recovery stages, the neutron irradiated SiC wasemployed to determine the maximum temperature of the parts running in the range of900-1600°C. The application test results demonstrated that the technique possesses aless than3%of the relative temperature errors.