Irradiation Defects in Neutron-irradiated 6H-SiC: Thermodynamic and High-temperature Recovery Kinetics

doi:10.15541/jim20250216

Abstract

Abstract:

Silicon carbide (SiC) is a promising material for nuclear reactor structures due to its excellent radiation resistance and high-temperature performance. The behavior of irradiation damage and the mechanisms of high-temperature recovery in SiC directly affect its service performance and longevity in nuclear environments. This study investigated effects of neutron irradiation on properties of 6H-SiC, with a particular focus on high-temperature recovery mechanisms of irradiation-induced defects. Specifically, defect evolution and thermodynamic responses in nitrogen-doped (N_D≈3.0×10¹⁹ cm^-3) 6H-SiC subjected to neutron irradiation at about 150 ℃ and a fluence of 2.58×10²⁰ n/cm² followed by isochronal annealing were examined. Integrated techniques and first-principles calculations were employed to comprehensively analyze its structural and property evolution. The key findings were as follows. (1) Significant lattice swelling was observed during the irradiation, with a swelling rate of 0.416% along the a-axis, 0.430% along the c-axis, and 1.310% in the unit cell volume, while all maintaining integrity of the single-crystalline structure. (2) A 14.7% increase in specific heat capacity was recorded, with 375.4 J/g of stored irradiation energy being released during heating from 100 ℃ to 500 ℃. (3) A four-stage defect recovery kinetic model was proposed based on the recovery of lattice parameters and the evolution of Raman spectra: Stage I (room temperature (RT)-600 ℃), primarily dominated by close-range recombination of carbon Frenkel pairs driven by migration energy (E_a) of 0.14 eV; Stage II (600-850 ℃), recombination of silicon Frenkel pairs and migration of carbon interstitials (E_a=0.26 eV); Stage III (850-1200 ℃), lattice reconstruction (E_a=0.65 eV); Stage IV (1200-1500 ℃), long-range diffusion of carbon vacancies (V_C) and dissociation of N_CV_Si complexes (E_a=1.50 eV). (4) The presence of nitrogen-stabilized N_CV_Si defect configurations was confirmed by a characteristic emission peak at 826 nm (634 cm^-1 Raman shift) when excited with 785 nm light. This study quantitatively reveals the defect recovery pathways and migration energies in neutron-irradiated 6H-SiC, providing a critical foundation for evaluating radiation damage, predicting performance, and optimizing annealing processes in nuclear-grade SiC materials.

Key words: irradiation-induced energy storage, specific heat, Raman spectroscopy, defect luminescence, Arrhenius

CLC Number:

ZHU Fei, HAO Xujie, ZHANG Quangui, YAN Xinyue, LIU Hongfei, ZHANG Bo, LI Xin, LIU Defeng, TUO Yayong, ZHANG Shouchao. Irradiation Defects in Neutron-irradiated 6H-SiC: Thermodynamic and High-temperature Recovery Kinetics[J]. Journal of Inorganic Materials, 2026, 41(3): 311-321.

Figures/Tables 11

Fig. 1 Variations of (a, b) 6H-SiC unit cell parameters and (c, d) (006) crystal plane diffraction peak with annealing temperature

Fig. 2 TEM images and SAED patterns of 6H-SiC showing irradiation damage and annealing recovery (a) Unirradiated sample; (b) Irradiated sample; (c) 900 ℃ annealed sample after irradiation

Fig. 3 SEM images of 6H-SiC surface microstructures (a)Unirradiated sample; (b) Neutron-irradiated sample; (c-f) Annealed at (c) 600, (d) 900, (e) 1200 and (f) 1500 ℃

Fig. 4 (a) TG and (b) DSC curves of 6H-SiC

Fig. 5 Temperature dependence of specific heat capacity for neutron-irradiated and annealed 6H-SiC at different temperatures (a) 100-300 ℃; (b) 600-1500 ℃

Fig. 6 Impact of vacancy and interstitial defects on lattice specific heat of SiC

Fig. 7 (a1, b1, c1, d1) C1s, (a2, b2, c2, d2) Si2p and (a3, b3, c3, d3) O1s XPS spectra of 6H-SiC (a1-a3) Unirradiated; (b1-b3) Irradiated; (c1-c3) Annealed at 600 ℃; (d1-d3) Annealed at 1500 ℃. Colorful figures are available on website

Fig. 8 Temperature-dependent evolution of Raman spectra of 6H-SiC (a) Unirradiated, neutron-irradiated, and annealed below 900 ℃; (b) Annealed at 900-1500 ℃

Fig. 9 Schematic diagrams of intrinsic defect states density and defect-induced photoluminescence mechanism in 6H-SiC (a) Total density of states with different intrinsic defects; (b) Defect-induced photoluminescence mechanism

Fig. 10 Variation of the natural logarithm change in unit cell volume (lnV-lnV0) of 6H-SiC with annealing time during isothermal annealing at 300-1500 ℃

Fig. 11 Arrhenius plots of the unit cell volume recovery rate for 6H-SiC as a function of annealing temperature

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