Recovery behavior of point defects after low-dose neutron irradiation at ∼423 K of sintered 6H–SiC by lattice parameter and macroscopic length measurements

Abstract

To evaluate neutron-irradiation-induced crystalline defects and its thermal stability, α-SiC sintered bodies consisting of mainly 6H polytype were neutron irradiated using the Japan Materials Testing Reactor up to 1.9×1023n/m2 (E>0.1MeV) at a low temperature of ∼423K. Due to very low dose irradiation at low temperature, expected defects induced into crystalline lattice should only be simple point defects. Changes in the lattice parameters and macroscopic lengths resulting from post-irradiation isothermal annealing up to 6h between room temperature and 1673K were measured. Macroscopic volume swelling of α-SiC specimens coincided well to those of unit cell volume changes, indicating the presence of only simple defects. The recovery behavior of the macroscopic length and lattice parameters showed almost the same tendencies, although residual changes in the c-axis length slightly exceeded that of the a-axis length at temperatures lower than 1273K. Difference in these axes lengths diminished at temperatures above 1273K. Calculation of activation energies, obtained from precise length measurement using a dilatometer during each isothermal annealing step, revealed that length recovery behavior between 473 and 1573K could almost be completely explained by a first-order reaction, and three stages with activation energies of 0.14, 0.26, and 1.13eV. Changes in activation energy were related to the behavior of lattice parameter changes. The results indicated the presence of several kinds of point defects, some of which induced anisotropic lattice expansion.